selftests/bpf: Add a test for objects stuck in free_by_rcu_ttracegrafted

Delete all elements of BPF_F_NO_PREALLOC hash map in one batch. The first
free_bulk() starts RCU tasks trace GP and the rest of the elements are
freed while it's in flight. Wait for call_rcu_ttrace_in_progress to clear
in bpf_mem_cache of every cpu and check that free_by_rcu_ttrace and
waiting_for_gp_ttrace lists are empty.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20260930095920.601738-4-alexei.starovoitov@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

1 files changed, 1531 insertions, 0 deletions

diff --git a/fs/file.c b/fs/file.c
new file mode 100644
index 000000000..628ca07dc
--- /dev/null
+++ b/fs/file.c
@@ -0,0 +1,1531 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/file.c
+ *
+ *  Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
+ *
+ *  Manage the dynamic fd arrays in the process files_struct.
+ */
+
+#include <linux/syscalls.h>
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/slab.h>
+#include <linux/file.h>
+#include <linux/fdtable.h>
+#include <linux/bitops.h>
+#include <linux/spinlock.h>
+#include <linux/rcupdate.h>
+#include <linux/close_range.h>
+#include <linux/file_ref.h>
+#include <net/sock.h>
+#include <linux/init_task.h>
+
+#include "internal.h"
+
+static noinline bool __file_ref_put_badval(file_ref_t *ref, unsigned long cnt)
+{
+	/*
+	 * If the reference count was already in the dead zone, then this
+	 * put() operation is imbalanced. Warn, put the reference count back to
+	 * DEAD and tell the caller to not deconstruct the object.
+	 */
+	if (WARN_ONCE(cnt >= FILE_REF_RELEASED, "imbalanced put on file reference count")) {
+		atomic_long_set(&ref->refcnt, FILE_REF_DEAD);
+		return false;
+	}
+
+	/*
+	 * This is a put() operation on a saturated refcount. Restore the
+	 * mean saturation value and tell the caller to not deconstruct the
+	 * object.
+	 */
+	if (cnt > FILE_REF_MAXREF)
+		atomic_long_set(&ref->refcnt, FILE_REF_SATURATED);
+	return false;
+}
+
+/**
+ * __file_ref_put - Slowpath of file_ref_put()
+ * @ref:	Pointer to the reference count
+ * @cnt:	Current reference count
+ *
+ * Invoked when the reference count is outside of the valid zone.
+ *
+ * Return:
+ *	True if this was the last reference with no future references
+ *	possible. This signals the caller that it can safely schedule the
+ *	object, which is protected by the reference counter, for
+ *	deconstruction.
+ *
+ *	False if there are still active references or the put() raced
+ *	with a concurrent get()/put() pair. Caller is not allowed to
+ *	deconstruct the protected object.
+ */
+bool __file_ref_put(file_ref_t *ref, unsigned long cnt)
+{
+	/* Did this drop the last reference? */
+	if (likely(cnt == FILE_REF_NOREF)) {
+		/*
+		 * Carefully try to set the reference count to FILE_REF_DEAD.
+		 *
+		 * This can fail if a concurrent get() operation has
+		 * elevated it again or the corresponding put() even marked
+		 * it dead already. Both are valid situations and do not
+		 * require a retry. If this fails the caller is not
+		 * allowed to deconstruct the object.
+		 */
+		if (!atomic_long_try_cmpxchg_release(&ref->refcnt, &cnt, FILE_REF_DEAD))
+			return false;
+
+		/*
+		 * The caller can safely schedule the object for
+		 * deconstruction. Provide acquire ordering.
+		 */
+		smp_acquire__after_ctrl_dep();
+		return true;
+	}
+
+	return __file_ref_put_badval(ref, cnt);
+}
+EXPORT_SYMBOL_GPL(__file_ref_put);
+
+unsigned int sysctl_nr_open __read_mostly = 1024*1024;
+unsigned int sysctl_nr_open_min = BITS_PER_LONG;
+/* our min() is unusable in constant expressions ;-/ */
+#define __const_min(x, y) ((x) < (y) ? (x) : (y))
+unsigned int sysctl_nr_open_max =
+	__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;
+
+static void __free_fdtable(struct fdtable *fdt)
+{
+	kvfree(fdt->fd);
+	kvfree(fdt->open_fds);
+	kfree(fdt);
+}
+
+static void free_fdtable_rcu(struct rcu_head *rcu)
+{
+	__free_fdtable(container_of(rcu, struct fdtable, rcu));
+}
+
+#define BITBIT_NR(nr)	BITS_TO_LONGS(BITS_TO_LONGS(nr))
+#define BITBIT_SIZE(nr)	(BITBIT_NR(nr) * sizeof(long))
+
+#define fdt_words(fdt) ((fdt)->max_fds / BITS_PER_LONG) // words in ->open_fds
+/*
+ * Copy 'count' fd bits from the old table to the new table and clear the extra
+ * space if any.  This does not copy the file pointers.  Called with the files
+ * spinlock held for write.
+ */
+static inline void copy_fd_bitmaps(struct fdtable *nfdt, struct fdtable *ofdt,
+			    unsigned int copy_words)
+{
+	unsigned int nwords = fdt_words(nfdt);
+
+	bitmap_copy_and_extend(nfdt->open_fds, ofdt->open_fds,
+			copy_words * BITS_PER_LONG, nwords * BITS_PER_LONG);
+	bitmap_copy_and_extend(nfdt->close_on_exec, ofdt->close_on_exec,
+			copy_words * BITS_PER_LONG, nwords * BITS_PER_LONG);
+	bitmap_copy_and_extend(nfdt->full_fds_bits, ofdt->full_fds_bits,
+			copy_words, nwords);
+}
+
+/*
+ * Copy all file descriptors from the old table to the new, expanded table and
+ * clear the extra space.  Called with the files spinlock held for write.
+ */
+static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
+{
+	size_t cpy, set;
+
+	BUG_ON(nfdt->max_fds < ofdt->max_fds);
+
+	cpy = ofdt->max_fds * sizeof(struct file *);
+	set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
+	memcpy(nfdt->fd, ofdt->fd, cpy);
+	memset((char *)nfdt->fd + cpy, 0, set);
+
+	copy_fd_bitmaps(nfdt, ofdt, fdt_words(ofdt));
+}
+
+/*
+ * Note how the fdtable bitmap allocations very much have to be a multiple of
+ * BITS_PER_LONG. This is not only because we walk those things in chunks of
+ * 'unsigned long' in some places, but simply because that is how the Linux
+ * kernel bitmaps are defined to work: they are not "bits in an array of bytes",
+ * they are very much "bits in an array of unsigned long".
+ */
+static struct fdtable *alloc_fdtable(unsigned int slots_wanted)
+{
+	struct fdtable *fdt;
+	unsigned int nr;
+	void *data;
+
+	/*
+	 * Figure out how many fds we actually want to support in this fdtable.
+	 * Allocation steps are keyed to the size of the fdarray, since it
+	 * grows far faster than any of the other dynamic data. We try to fit
+	 * the fdarray into comfortable page-tuned chunks: starting at 1024B
+	 * and growing in powers of two from there on.  Since we called only
+	 * with slots_wanted > BITS_PER_LONG (embedded instance in files->fdtab
+	 * already gives BITS_PER_LONG slots), the above boils down to
+	 * 1.  use the smallest power of two large enough to give us that many
+	 * slots.
+	 * 2.  on 32bit skip 64 and 128 - the minimal capacity we want there is
+	 * 256 slots (i.e. 1Kb fd array).
+	 * 3.  on 64bit don't skip anything, 1Kb fd array means 128 slots there
+	 * and we are never going to be asked for 64 or less.
+	 */
+	if (IS_ENABLED(CONFIG_32BIT) && slots_wanted < 256)
+		nr = 256;
+	else
+		nr = roundup_pow_of_two(slots_wanted);
+	/*
+	 * Note that this can drive nr *below* what we had passed if sysctl_nr_open
+	 * had been set lower between the check in expand_files() and here.
+	 *
+	 * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
+	 * bitmaps handling below becomes unpleasant, to put it mildly...
+	 */
+	if (unlikely(nr > sysctl_nr_open)) {
+		nr = round_down(sysctl_nr_open, BITS_PER_LONG);
+		if (nr < slots_wanted)
+			return ERR_PTR(-EMFILE);
+	}
+
+	/*
+	 * Check if the allocation size would exceed INT_MAX. kvmalloc_array()
+	 * and kvmalloc() will warn if the allocation size is greater than
+	 * INT_MAX, as filp_cache objects are not __GFP_NOWARN.
+	 *
+	 * This can happen when sysctl_nr_open is set to a very high value and
+	 * a process tries to use a file descriptor near that limit. For example,
+	 * if sysctl_nr_open is set to 1073741816 (0x3ffffff8) - which is what
+	 * systemd typically sets it to - then trying to use a file descriptor
+	 * close to that value will require allocating a file descriptor table
+	 * that exceeds 8GB in size.
+	 */
+	if (unlikely(nr > INT_MAX / sizeof(struct file *)))
+		return ERR_PTR(-EMFILE);
+
+	fdt = kmalloc_obj(struct fdtable, GFP_KERNEL_ACCOUNT);
+	if (!fdt)
+		goto out;
+	fdt->max_fds = nr;
+	data = kvmalloc_objs(struct file *, nr, GFP_KERNEL_ACCOUNT);
+	if (!data)
+		goto out_fdt;
+	fdt->fd = data;
+
+	data = kvmalloc(max_t(size_t,
+				 2 * nr / BITS_PER_BYTE + BITBIT_SIZE(nr), L1_CACHE_BYTES),
+				 GFP_KERNEL_ACCOUNT);
+	if (!data)
+		goto out_arr;
+	fdt->open_fds = data;
+	data += nr / BITS_PER_BYTE;
+	fdt->close_on_exec = data;
+	data += nr / BITS_PER_BYTE;
+	fdt->full_fds_bits = data;
+
+	return fdt;
+
+out_arr:
+	kvfree(fdt->fd);
+out_fdt:
+	kfree(fdt);
+out:
+	return ERR_PTR(-ENOMEM);
+}
+
+/*
+ * Expand the file descriptor table.
+ * This function will allocate a new fdtable and both fd array and fdset, of
+ * the given size.
+ * Return <0 error code on error; 0 on successful completion.
+ * The files->file_lock should be held on entry, and will be held on exit.
+ */
+static int expand_fdtable(struct files_struct *files, unsigned int nr)
+	__releases(files->file_lock)
+	__acquires(files->file_lock)
+{
+	struct fdtable *new_fdt, *cur_fdt;
+
+	spin_unlock(&files->file_lock);
+	new_fdt = alloc_fdtable(nr + 1);
+
+	/* make sure all fd_install() have seen resize_in_progress
+	 * or have finished their rcu_read_lock_sched() section.
+	 */
+	if (atomic_read(&files->count) > 1)
+		synchronize_rcu();
+
+	spin_lock(&files->file_lock);
+	if (IS_ERR(new_fdt))
+		return PTR_ERR(new_fdt);
+	cur_fdt = files_fdtable(files);
+	BUG_ON(nr < cur_fdt->max_fds);
+	copy_fdtable(new_fdt, cur_fdt);
+	rcu_assign_pointer(files->fdt, new_fdt);
+	if (cur_fdt != &files->fdtab)
+		call_rcu(&cur_fdt->rcu, free_fdtable_rcu);
+	/* coupled with smp_rmb() in fd_install() */
+	smp_wmb();
+	return 0;
+}
+
+/*
+ * Expand files.
+ * This function will expand the file structures, if the requested size exceeds
+ * the current capacity and there is room for expansion.
+ * Return <0 error code on error; 0 on success.
+ * The files->file_lock should be held on entry, and will be held on exit.
+ */
+static int expand_files(struct files_struct *files, unsigned int nr)
+	__releases(files->file_lock)
+	__acquires(files->file_lock)
+{
+	struct fdtable *fdt;
+	int error;
+
+repeat:
+	fdt = files_fdtable(files);
+
+	/* Do we need to expand? */
+	if (nr < fdt->max_fds)
+		return 0;
+
+	if (unlikely(files->resize_in_progress)) {
+		spin_unlock(&files->file_lock);
+		wait_event(files->resize_wait, !files->resize_in_progress);
+		spin_lock(&files->file_lock);
+		goto repeat;
+	}
+
+	/* Can we expand? */
+	if (unlikely(nr >= sysctl_nr_open))
+		return -EMFILE;
+
+	/* All good, so we try */
+	files->resize_in_progress = true;
+	error = expand_fdtable(files, nr);
+	files->resize_in_progress = false;
+
+	wake_up_all(&files->resize_wait);
+	return error;
+}
+
+static inline void __set_close_on_exec(unsigned int fd, struct fdtable *fdt,
+				       bool set)
+{
+	if (set) {
+		__set_bit(fd, fdt->close_on_exec);
+	} else {
+		if (test_bit(fd, fdt->close_on_exec))
+			__clear_bit(fd, fdt->close_on_exec);
+	}
+}
+
+static inline void __set_open_fd(unsigned int fd, struct fdtable *fdt, bool set)
+{
+	__set_bit(fd, fdt->open_fds);
+	__set_close_on_exec(fd, fdt, set);
+	fd /= BITS_PER_LONG;
+	if (!~fdt->open_fds[fd])
+		__set_bit(fd, fdt->full_fds_bits);
+}
+
+static inline void __clear_open_fd(unsigned int fd, struct fdtable *fdt)
+{
+	__clear_bit(fd, fdt->open_fds);
+	fd /= BITS_PER_LONG;
+	if (test_bit(fd, fdt->full_fds_bits))
+		__clear_bit(fd, fdt->full_fds_bits);
+}
+
+static inline bool fd_is_open(unsigned int fd, const struct fdtable *fdt)
+{
+	return test_bit(fd, fdt->open_fds);
+}
+
+/*
+ * Note that a sane fdtable size always has to be a multiple of
+ * BITS_PER_LONG, since we have bitmaps that are sized by this.
+ *
+ * punch_hole is optional - when close_range() is asked to unshare
+ * and close, we don't need to copy descriptors in that range, so
+ * a smaller cloned descriptor table might suffice if the last
+ * currently opened descriptor falls into that range.
+ */
+static unsigned int sane_fdtable_size(struct fdtable *fdt, struct fd_range *punch_hole)
+{
+	unsigned int last = find_last_bit(fdt->open_fds, fdt->max_fds);
+
+	if (last == fdt->max_fds)
+		return NR_OPEN_DEFAULT;
+	if (punch_hole && punch_hole->to >= last && punch_hole->from <= last) {
+		last = find_last_bit(fdt->open_fds, punch_hole->from);
+		if (last == punch_hole->from)
+			return NR_OPEN_DEFAULT;
+	}
+	return ALIGN(last + 1, BITS_PER_LONG);
+}
+
+/*
+ * Allocate a new descriptor table and copy contents from the passed in
+ * instance.  Returns a pointer to cloned table on success, ERR_PTR()
+ * on failure.  For 'punch_hole' see sane_fdtable_size().
+ */
+struct files_struct *dup_fd(struct files_struct *oldf, struct fd_range *punch_hole)
+{
+	struct files_struct *newf;
+	struct file **old_fds, **new_fds;
+	unsigned int open_files, i;
+	struct fdtable *old_fdt, *new_fdt;
+
+	newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
+	if (!newf)
+		return ERR_PTR(-ENOMEM);
+
+	atomic_set(&newf->count, 1);
+
+	spin_lock_init(&newf->file_lock);
+	newf->resize_in_progress = false;
+	init_waitqueue_head(&newf->resize_wait);
+	newf->next_fd = 0;
+	new_fdt = &newf->fdtab;
+	new_fdt->max_fds = NR_OPEN_DEFAULT;
+	new_fdt->close_on_exec = newf->close_on_exec_init;
+	new_fdt->open_fds = newf->open_fds_init;
+	new_fdt->full_fds_bits = newf->full_fds_bits_init;
+	new_fdt->fd = &newf->fd_array[0];
+
+	spin_lock(&oldf->file_lock);
+	old_fdt = files_fdtable(oldf);
+	open_files = sane_fdtable_size(old_fdt, punch_hole);
+
+	/*
+	 * Check whether we need to allocate a larger fd array and fd set.
+	 */
+	while (unlikely(open_files > new_fdt->max_fds)) {
+		spin_unlock(&oldf->file_lock);
+
+		if (new_fdt != &newf->fdtab)
+			__free_fdtable(new_fdt);
+
+		new_fdt = alloc_fdtable(open_files);
+		if (IS_ERR(new_fdt)) {
+			kmem_cache_free(files_cachep, newf);
+			return ERR_CAST(new_fdt);
+		}
+
+		/*
+		 * Reacquire the oldf lock and a pointer to its fd table
+		 * who knows it may have a new bigger fd table. We need
+		 * the latest pointer.
+		 */
+		spin_lock(&oldf->file_lock);
+		old_fdt = files_fdtable(oldf);
+		open_files = sane_fdtable_size(old_fdt, punch_hole);
+	}
+
+	copy_fd_bitmaps(new_fdt, old_fdt, open_files / BITS_PER_LONG);
+
+	old_fds = old_fdt->fd;
+	new_fds = new_fdt->fd;
+
+	/*
+	 * We may be racing against fd allocation from other threads using this
+	 * files_struct, despite holding ->file_lock.
+	 *
+	 * alloc_fd() might have already claimed a slot, while fd_install()
+	 * did not populate it yet. Note the latter operates locklessly, so
+	 * the file can show up as we are walking the array below.
+	 *
+	 * At the same time we know no files will disappear as all other
+	 * operations take the lock.
+	 *
+	 * Instead of trying to placate userspace racing with itself, we
+	 * ref the file if we see it and mark the fd slot as unused otherwise.
+	 */
+	for (i = open_files; i != 0; i--) {
+		struct file *f = rcu_dereference_raw(*old_fds++);
+		if (f) {
+			get_file(f);
+		} else {
+			__clear_open_fd(open_files - i, new_fdt);
+		}
+		rcu_assign_pointer(*new_fds++, f);
+	}
+	spin_unlock(&oldf->file_lock);
+
+	/* clear the remainder */
+	memset(new_fds, 0, (new_fdt->max_fds - open_files) * sizeof(struct file *));
+
+	rcu_assign_pointer(newf->fdt, new_fdt);
+
+	return newf;
+}
+
+static struct fdtable *close_files(struct files_struct * files)
+{
+	/*
+	 * It is safe to dereference the fd table without RCU or
+	 * ->file_lock because this is the last reference to the
+	 * files structure.
+	 */
+	struct fdtable *fdt = rcu_dereference_raw(files->fdt);
+	unsigned int i, j = 0;
+
+	for (;;) {
+		unsigned long set;
+		i = j * BITS_PER_LONG;
+		if (i >= fdt->max_fds)
+			break;
+		set = fdt->open_fds[j++];
+		while (set) {
+			if (set & 1) {
+				struct file *file = fdt->fd[i];
+				if (file) {
+					filp_close(file, files);
+					cond_resched();
+				}
+			}
+			i++;
+			set >>= 1;
+		}
+	}
+
+	return fdt;
+}
+
+void put_files_struct(struct files_struct *files)
+{
+	if (atomic_dec_and_test(&files->count)) {
+		struct fdtable *fdt = close_files(files);
+
+		/* free the arrays if they are not embedded */
+		if (fdt != &files->fdtab)
+			__free_fdtable(fdt);
+		kmem_cache_free(files_cachep, files);
+	}
+}
+
+void exit_files(struct task_struct *tsk)
+{
+	struct files_struct * files = tsk->files;
+
+	if (files) {
+		task_lock(tsk);
+		tsk->files = NULL;
+		task_unlock(tsk);
+		put_files_struct(files);
+	}
+}
+
+struct files_struct init_files = {
+	.count		= ATOMIC_INIT(1),
+	.fdt		= &init_files.fdtab,
+	.fdtab		= {
+		.max_fds	= NR_OPEN_DEFAULT,
+		.fd		= &init_files.fd_array[0],
+		.close_on_exec	= init_files.close_on_exec_init,
+		.open_fds	= init_files.open_fds_init,
+		.full_fds_bits	= init_files.full_fds_bits_init,
+	},
+	.file_lock	= __SPIN_LOCK_UNLOCKED(init_files.file_lock),
+	.resize_wait	= __WAIT_QUEUE_HEAD_INITIALIZER(init_files.resize_wait),
+};
+
+static unsigned int find_next_fd(struct fdtable *fdt, unsigned int start)
+{
+	unsigned int maxfd = fdt->max_fds; /* always multiple of BITS_PER_LONG */
+	unsigned int max_fds_words = maxfd / BITS_PER_LONG;
+	unsigned int fds_word_idx = start / BITS_PER_LONG;
+	unsigned int bit;
+
+	/*
+	 * Try to avoid looking at the second level bitmap
+	 */
+	bit = find_next_zero_bit(&fdt->open_fds[fds_word_idx], BITS_PER_LONG,
+				 start & (BITS_PER_LONG - 1));
+	if (bit < BITS_PER_LONG)
+		return bit + (fds_word_idx * BITS_PER_LONG);
+
+	bit = BITS_PER_LONG *
+		find_next_zero_bit(fdt->full_fds_bits, max_fds_words, fds_word_idx + 1);
+	if (bit >= maxfd)
+		return maxfd;
+	return find_next_zero_bit(fdt->open_fds, maxfd, bit);
+}
+
+/*
+ * allocate a file descriptor, mark it busy.
+ */
+static int alloc_fd(unsigned start, unsigned end, unsigned flags)
+{
+	struct files_struct *files = current->files;
+	unsigned int fd;
+	int error;
+	struct fdtable *fdt;
+
+	spin_lock(&files->file_lock);
+repeat:
+	fdt = files_fdtable(files);
+	fd = start;
+	if (fd < files->next_fd)
+		fd = files->next_fd;
+
+	if (likely(fd < fdt->max_fds))
+		fd = find_next_fd(fdt, fd);
+
+	/*
+	 * N.B. For clone tasks sharing a files structure, this test
+	 * will limit the total number of files that can be opened.
+	 */
+	error = -EMFILE;
+	if (unlikely(fd >= end))
+		goto out;
+
+	if (unlikely(fd >= fdt->max_fds)) {
+		error = expand_files(files, fd);
+		if (error < 0)
+			goto out;
+
+		goto repeat;
+	}
+
+	if (start <= files->next_fd)
+		files->next_fd = fd + 1;
+
+	__set_open_fd(fd, fdt, flags & O_CLOEXEC);
+	error = fd;
+	VFS_BUG_ON(rcu_access_pointer(fdt->fd[fd]) != NULL);
+
+out:
+	spin_unlock(&files->file_lock);
+	return error;
+}
+
+int __get_unused_fd_flags(unsigned flags, unsigned long nofile)
+{
+	return alloc_fd(0, nofile, flags);
+}
+
+int get_unused_fd_flags(unsigned flags)
+{
+	return __get_unused_fd_flags(flags, rlimit(RLIMIT_NOFILE));
+}
+EXPORT_SYMBOL(get_unused_fd_flags);
+
+static void __put_unused_fd(struct files_struct *files, unsigned int fd)
+{
+	struct fdtable *fdt = files_fdtable(files);
+	__clear_open_fd(fd, fdt);
+	if (fd < files->next_fd)
+		files->next_fd = fd;
+}
+
+void put_unused_fd(unsigned int fd)
+{
+	struct files_struct *files = current->files;
+	spin_lock(&files->file_lock);
+	__put_unused_fd(files, fd);
+	spin_unlock(&files->file_lock);
+}
+
+EXPORT_SYMBOL(put_unused_fd);
+
+/*
+ * Install a file pointer in the fd array while it is being resized.
+ *
+ * We need to make sure our update to the array does not get lost as the resizing
+ * thread can be copying the content as we modify it.
+ *
+ * We have two ways to do it:
+ * - go off CPU waiting for resize_in_progress to clear
+ * - take the spin lock
+ *
+ * The latter is trivial to implement and saves us from having to might_sleep()
+ * for debugging purposes.
+ *
+ * This is moved out of line from fd_install() to convince gcc to optimize that
+ * routine better.
+ */
+static void noinline fd_install_slowpath(unsigned int fd, struct file *file)
+{
+	struct files_struct *files = current->files;
+	struct fdtable *fdt;
+
+	spin_lock(&files->file_lock);
+	fdt = files_fdtable(files);
+	VFS_BUG_ON(rcu_access_pointer(fdt->fd[fd]) != NULL);
+	rcu_assign_pointer(fdt->fd[fd], file);
+	spin_unlock(&files->file_lock);
+}
+
+/**
+ * fd_install - install a file pointer in the fd array
+ * @fd: file descriptor to install the file in
+ * @file: the file to install
+ *
+ * This consumes the "file" refcount, so callers should treat it
+ * as if they had called fput(file).
+ */
+void fd_install(unsigned int fd, struct file *file)
+{
+	struct files_struct *files = current->files;
+	struct fdtable *fdt;
+
+	if (WARN_ON_ONCE(unlikely(file->f_mode & FMODE_BACKING)))
+		return;
+
+	rcu_read_lock_sched();
+	if (unlikely(files->resize_in_progress)) {
+		rcu_read_unlock_sched();
+		fd_install_slowpath(fd, file);
+		return;
+	}
+	/* coupled with smp_wmb() in expand_fdtable() */
+	smp_rmb();
+	fdt = rcu_dereference_sched(files->fdt);
+	VFS_BUG_ON(rcu_access_pointer(fdt->fd[fd]) != NULL);
+	rcu_assign_pointer(fdt->fd[fd], file);
+	rcu_read_unlock_sched();
+}
+
+EXPORT_SYMBOL(fd_install);
+
+/**
+ * file_close_fd_locked - return file associated with fd
+ * @files: file struct to retrieve file from
+ * @fd: file descriptor to retrieve file for
+ *
+ * Doesn't take a separate reference count.
+ *
+ * Context: files_lock must be held.
+ *
+ * Returns: The file associated with @fd (NULL if @fd is not open)
+ */
+struct file *file_close_fd_locked(struct files_struct *files, unsigned fd)
+{
+	struct fdtable *fdt = files_fdtable(files);
+	struct file *file;
+
+	lockdep_assert_held(&files->file_lock);
+
+	if (fd >= fdt->max_fds)
+		return NULL;
+
+	fd = array_index_nospec(fd, fdt->max_fds);
+	file = rcu_dereference_raw(fdt->fd[fd]);
+	if (file) {
+		rcu_assign_pointer(fdt->fd[fd], NULL);
+		__put_unused_fd(files, fd);
+	}
+	return file;
+}
+
+int close_fd(unsigned fd)
+{
+	struct files_struct *files = current->files;
+	struct file *file;
+
+	spin_lock(&files->file_lock);
+	file = file_close_fd_locked(files, fd);
+	spin_unlock(&files->file_lock);
+	if (!file)
+		return -EBADF;
+
+	return filp_close(file, files);
+}
+EXPORT_SYMBOL(close_fd);
+
+/**
+ * last_fd - return last valid index into fd table
+ * @fdt: File descriptor table.
+ *
+ * Context: Either rcu read lock or files_lock must be held.
+ *
+ * Returns: Last valid index into fdtable.
+ */
+static inline unsigned last_fd(struct fdtable *fdt)
+{
+	return fdt->max_fds - 1;
+}
+
+static inline void __range_cloexec(struct files_struct *cur_fds,
+				   unsigned int fd, unsigned int max_fd)
+{
+	struct fdtable *fdt;
+
+	/* make sure we're using the correct maximum value */
+	spin_lock(&cur_fds->file_lock);
+	fdt = files_fdtable(cur_fds);
+	max_fd = min(last_fd(fdt), max_fd);
+	if (fd <= max_fd)
+		bitmap_set(fdt->close_on_exec, fd, max_fd - fd + 1);
+	spin_unlock(&cur_fds->file_lock);
+}
+
+static inline void __range_close(struct files_struct *files, unsigned int fd,
+				 unsigned int max_fd)
+{
+	struct file *file;
+	struct fdtable *fdt;
+	unsigned n;
+
+	spin_lock(&files->file_lock);
+	fdt = files_fdtable(files);
+	n = last_fd(fdt);
+	max_fd = min(max_fd, n);
+
+	for (fd = find_next_bit(fdt->open_fds, max_fd + 1, fd);
+	     fd <= max_fd;
+	     fd = find_next_bit(fdt->open_fds, max_fd + 1, fd + 1)) {
+		file = file_close_fd_locked(files, fd);
+		if (file) {
+			spin_unlock(&files->file_lock);
+			filp_close(file, files);
+			cond_resched();
+			spin_lock(&files->file_lock);
+			fdt = files_fdtable(files);
+		} else if (need_resched()) {
+			spin_unlock(&files->file_lock);
+			cond_resched();
+			spin_lock(&files->file_lock);
+			fdt = files_fdtable(files);
+		}
+	}
+	spin_unlock(&files->file_lock);
+}
+
+/**
+ * sys_close_range() - Close all file descriptors in a given range.
+ *
+ * @fd:     starting file descriptor to close
+ * @max_fd: last file descriptor to close
+ * @flags:  CLOSE_RANGE flags.
+ *
+ * This closes a range of file descriptors. All file descriptors
+ * from @fd up to and including @max_fd are closed.
+ * Currently, errors to close a given file descriptor are ignored.
+ */
+SYSCALL_DEFINE3(close_range, unsigned int, fd, unsigned int, max_fd,
+		unsigned int, flags)
+{
+	struct task_struct *me = current;
+	struct files_struct *cur_fds = me->files, *fds = NULL;
+
+	if (flags & ~(CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC))
+		return -EINVAL;
+
+	if (fd > max_fd)
+		return -EINVAL;
+
+	if ((flags & CLOSE_RANGE_UNSHARE) && atomic_read(&cur_fds->count) > 1) {
+		struct fd_range range = {fd, max_fd}, *punch_hole = &range;
+
+		/*
+		 * If the caller requested all fds to be made cloexec we always
+		 * copy all of the file descriptors since they still want to
+		 * use them.
+		 */
+		if (flags & CLOSE_RANGE_CLOEXEC)
+			punch_hole = NULL;
+
+		fds = dup_fd(cur_fds, punch_hole);
+		if (IS_ERR(fds))
+			return PTR_ERR(fds);
+		/*
+		 * We used to share our file descriptor table, and have now
+		 * created a private one, make sure we're using it below.
+		 */
+		swap(cur_fds, fds);
+	}
+
+	if (flags & CLOSE_RANGE_CLOEXEC)
+		__range_cloexec(cur_fds, fd, max_fd);
+	else
+		__range_close(cur_fds, fd, max_fd);
+
+	if (fds) {
+		/*
+		 * We're done closing the files we were supposed to. Time to install
+		 * the new file descriptor table and drop the old one.
+		 */
+		task_lock(me);
+		me->files = cur_fds;
+		task_unlock(me);
+		put_files_struct(fds);
+	}
+
+	return 0;
+}
+
+/**
+ * file_close_fd - return file associated with fd
+ * @fd: file descriptor to retrieve file for
+ *
+ * Doesn't take a separate reference count.
+ *
+ * Returns: The file associated with @fd (NULL if @fd is not open)
+ */
+struct file *file_close_fd(unsigned int fd)
+{
+	struct files_struct *files = current->files;
+	struct file *file;
+
+	spin_lock(&files->file_lock);
+	file = file_close_fd_locked(files, fd);
+	spin_unlock(&files->file_lock);
+
+	return file;
+}
+
+void do_close_on_exec(struct files_struct *files)
+{
+	unsigned i;
+	struct fdtable *fdt;
+
+	/* exec unshares first */
+	spin_lock(&files->file_lock);
+	for (i = 0; ; i++) {
+		unsigned long set;
+		unsigned fd = i * BITS_PER_LONG;
+		fdt = files_fdtable(files);
+		if (fd >= fdt->max_fds)
+			break;
+		set = fdt->close_on_exec[i];
+		if (!set)
+			continue;
+		fdt->close_on_exec[i] = 0;
+		for ( ; set ; fd++, set >>= 1) {
+			struct file *file;
+			if (!(set & 1))
+				continue;
+			file = fdt->fd[fd];
+			if (!file)
+				continue;
+			rcu_assign_pointer(fdt->fd[fd], NULL);
+			__put_unused_fd(files, fd);
+			spin_unlock(&files->file_lock);
+			filp_close(file, files);
+			cond_resched();
+			spin_lock(&files->file_lock);
+		}
+
+	}
+	spin_unlock(&files->file_lock);
+}
+
+static struct file *__get_file_rcu(struct file __rcu **f)
+{
+	struct file __rcu *file;
+	struct file __rcu *file_reloaded;
+	struct file __rcu *file_reloaded_cmp;
+
+	file = rcu_dereference_raw(*f);
+	if (!file)
+		return NULL;
+
+	if (unlikely(!file_ref_get(&file->f_ref)))
+		return ERR_PTR(-EAGAIN);
+
+	file_reloaded = rcu_dereference_raw(*f);
+
+	/*
+	 * Ensure that all accesses have a dependency on the load from
+	 * rcu_dereference_raw() above so we get correct ordering
+	 * between reuse/allocation and the pointer check below.
+	 */
+	file_reloaded_cmp = file_reloaded;
+	OPTIMIZER_HIDE_VAR(file_reloaded_cmp);
+
+	/*
+	 * file_ref_get() above provided a full memory barrier when we
+	 * acquired a reference.
+	 *
+	 * This is paired with the write barrier from assigning to the
+	 * __rcu protected file pointer so that if that pointer still
+	 * matches the current file, we know we have successfully
+	 * acquired a reference to the right file.
+	 *
+	 * If the pointers don't match the file has been reallocated by
+	 * SLAB_TYPESAFE_BY_RCU.
+	 */
+	if (file == file_reloaded_cmp)
+		return file_reloaded;
+
+	fput(file);
+	return ERR_PTR(-EAGAIN);
+}
+
+/**
+ * get_file_rcu - try go get a reference to a file under rcu
+ * @f: the file to get a reference on
+ *
+ * This function tries to get a reference on @f carefully verifying that
+ * @f hasn't been reused.
+ *
+ * This function should rarely have to be used and only by users who
+ * understand the implications of SLAB_TYPESAFE_BY_RCU. Try to avoid it.
+ *
+ * Return: Returns @f with the reference count increased or NULL.
+ */
+struct file *get_file_rcu(struct file __rcu **f)
+{
+	for (;;) {
+		struct file __rcu *file;
+
+		file = __get_file_rcu(f);
+		if (!IS_ERR(file))
+			return file;
+	}
+}
+EXPORT_SYMBOL_GPL(get_file_rcu);
+
+/**
+ * get_file_active - try go get a reference to a file
+ * @f: the file to get a reference on
+ *
+ * In contast to get_file_rcu() the pointer itself isn't part of the
+ * reference counting.
+ *
+ * This function should rarely have to be used and only by users who
+ * understand the implications of SLAB_TYPESAFE_BY_RCU. Try to avoid it.
+ *
+ * Return: Returns @f with the reference count increased or NULL.
+ */
+struct file *get_file_active(struct file **f)
+{
+	struct file __rcu *file;
+
+	rcu_read_lock();
+	file = __get_file_rcu(f);
+	rcu_read_unlock();
+	if (IS_ERR(file))
+		file = NULL;
+	return file;
+}
+EXPORT_SYMBOL_GPL(get_file_active);
+
+static inline struct file *__fget_files_rcu(struct files_struct *files,
+       unsigned int fd, fmode_t mask)
+{
+	for (;;) {
+		struct file *file;
+		struct fdtable *fdt = rcu_dereference_raw(files->fdt);
+		struct file __rcu **fdentry;
+		unsigned long nospec_mask;
+
+		/* Mask is a 0 for invalid fd's, ~0 for valid ones */
+		nospec_mask = array_index_mask_nospec(fd, fdt->max_fds);
+
+		/*
+		 * fdentry points to the 'fd' offset, or fdt->fd[0].
+		 * Loading from fdt->fd[0] is always safe, because the
+		 * array always exists.
+		 */
+		fdentry = fdt->fd + (fd & nospec_mask);
+
+		/* Do the load, then mask any invalid result */
+		file = rcu_dereference_raw(*fdentry);
+		file = (void *)(nospec_mask & (unsigned long)file);
+		if (unlikely(!file))
+			return NULL;
+
+		/*
+		 * Ok, we have a file pointer that was valid at
+		 * some point, but it might have become stale since.
+		 *
+		 * We need to confirm it by incrementing the refcount
+		 * and then check the lookup again.
+		 *
+		 * file_ref_get() gives us a full memory barrier. We
+		 * only really need an 'acquire' one to protect the
+		 * loads below, but we don't have that.
+		 */
+		if (unlikely(!file_ref_get(&file->f_ref)))
+			continue;
+
+		/*
+		 * Such a race can take two forms:
+		 *
+		 *  (a) the file ref already went down to zero and the
+		 *      file hasn't been reused yet or the file count
+		 *      isn't zero but the file has already been reused.
+		 *
+		 *  (b) the file table entry has changed under us.
+		 *       Note that we don't need to re-check the 'fdt->fd'
+		 *       pointer having changed, because it always goes
+		 *       hand-in-hand with 'fdt'.
+		 *
+		 * If so, we need to put our ref and try again.
+		 */
+		if (unlikely(file != rcu_dereference_raw(*fdentry)) ||
+		    unlikely(rcu_dereference_raw(files->fdt) != fdt)) {
+			fput(file);
+			continue;
+		}
+
+		/*
+		 * This isn't the file we're looking for or we're not
+		 * allowed to get a reference to it.
+		 */
+		if (unlikely(file->f_mode & mask)) {
+			fput(file);
+			return NULL;
+		}
+
+		/*
+		 * Ok, we have a ref to the file, and checked that it
+		 * still exists.
+		 */
+		return file;
+	}
+}
+
+static struct file *__fget_files(struct files_struct *files, unsigned int fd,
+				 fmode_t mask)
+{
+	struct file *file;
+
+	rcu_read_lock();
+	file = __fget_files_rcu(files, fd, mask);
+	rcu_read_unlock();
+
+	return file;
+}
+
+static inline struct file *__fget(unsigned int fd, fmode_t mask)
+{
+	return __fget_files(current->files, fd, mask);
+}
+
+struct file *fget(unsigned int fd)
+{
+	return __fget(fd, FMODE_PATH);
+}
+EXPORT_SYMBOL(fget);
+
+struct file *fget_raw(unsigned int fd)
+{
+	return __fget(fd, 0);
+}
+EXPORT_SYMBOL(fget_raw);
+
+struct file *fget_task(struct task_struct *task, unsigned int fd)
+{
+	struct file *file = NULL;
+
+	task_lock(task);
+	if (task->files)
+		file = __fget_files(task->files, fd, 0);
+	task_unlock(task);
+
+	return file;
+}
+
+struct file *fget_task_next(struct task_struct *task, unsigned int *ret_fd)
+{
+	struct files_struct *files;
+	unsigned int fd = *ret_fd;
+	struct file *file = NULL;
+
+	task_lock(task);
+	files = task->files;
+	if (files) {
+		rcu_read_lock();
+		for (; fd < files_fdtable(files)->max_fds; fd++) {
+			file = __fget_files_rcu(files, fd, 0);
+			if (file)
+				break;
+		}
+		rcu_read_unlock();
+	}
+	task_unlock(task);
+	*ret_fd = fd;
+	return file;
+}
+EXPORT_SYMBOL(fget_task_next);
+
+/*
+ * Lightweight file lookup - no refcnt increment if fd table isn't shared.
+ *
+ * You can use this instead of fget if you satisfy all of the following
+ * conditions:
+ * 1) You must call fput_light before exiting the syscall and returning control
+ *    to userspace (i.e. you cannot remember the returned struct file * after
+ *    returning to userspace).
+ * 2) You must not call filp_close on the returned struct file * in between
+ *    calls to fget_light and fput_light.
+ * 3) You must not clone the current task in between the calls to fget_light
+ *    and fput_light.
+ *
+ * The fput_needed flag returned by fget_light should be passed to the
+ * corresponding fput_light.
+ *
+ * (As an exception to rule 2, you can call filp_close between fget_light and
+ * fput_light provided that you capture a real refcount with get_file before
+ * the call to filp_close, and ensure that this real refcount is fput *after*
+ * the fput_light call.)
+ *
+ * See also the documentation in rust/kernel/file.rs.
+ */
+static inline struct fd __fget_light(unsigned int fd, fmode_t mask)
+{
+	struct files_struct *files = current->files;
+	struct file *file;
+
+	/*
+	 * If another thread is concurrently calling close_fd() followed
+	 * by put_files_struct(), we must not observe the old table
+	 * entry combined with the new refcount - otherwise we could
+	 * return a file that is concurrently being freed.
+	 *
+	 * atomic_read_acquire() pairs with atomic_dec_and_test() in
+	 * put_files_struct().
+	 */
+	if (likely(atomic_read_acquire(&files->count) == 1)) {
+		file = files_lookup_fd_raw(files, fd);
+		if (!file || unlikely(file->f_mode & mask))
+			return EMPTY_FD;
+		return BORROWED_FD(file);
+	} else {
+		file = __fget_files(files, fd, mask);
+		if (!file)
+			return EMPTY_FD;
+		return CLONED_FD(file);
+	}
+}
+struct fd fdget(unsigned int fd)
+{
+	return __fget_light(fd, FMODE_PATH);
+}
+EXPORT_SYMBOL(fdget);
+
+struct fd fdget_raw(unsigned int fd)
+{
+	return __fget_light(fd, 0);
+}
+
+/*
+ * Try to avoid f_pos locking. We only need it if the
+ * file is marked for FMODE_ATOMIC_POS, and it can be
+ * accessed multiple ways.
+ *
+ * Always do it for directories, because pidfd_getfd()
+ * can make a file accessible even if it otherwise would
+ * not be, and for directories this is a correctness
+ * issue, not a "POSIX requirement".
+ */
+static inline bool file_needs_f_pos_lock(struct file *file)
+{
+	if (!(file->f_mode & FMODE_ATOMIC_POS))
+		return false;
+	if (__file_ref_read_raw(&file->f_ref) != FILE_REF_ONEREF)
+		return true;
+	if (file->f_op->iterate_shared)
+		return true;
+	return false;
+}
+
+bool file_seek_cur_needs_f_lock(struct file *file)
+{
+	if (!(file->f_mode & FMODE_ATOMIC_POS) && !file->f_op->iterate_shared)
+		return false;
+
+	/*
+	 * Note that we are not guaranteed to be called after fdget_pos() on
+	 * this file obj, in which case the caller is expected to provide the
+	 * appropriate locking.
+	 */
+
+	return true;
+}
+
+struct fd fdget_pos(unsigned int fd)
+{
+	struct fd f = fdget(fd);
+	struct file *file = fd_file(f);
+
+	if (likely(file) && file_needs_f_pos_lock(file)) {
+		f.word |= FDPUT_POS_UNLOCK;
+		mutex_lock(&file->f_pos_lock);
+	}
+	return f;
+}
+
+void __f_unlock_pos(struct file *f)
+{
+	mutex_unlock(&f->f_pos_lock);
+}
+
+/*
+ * We only lock f_pos if we have threads or if the file might be
+ * shared with another process. In both cases we'll have an elevated
+ * file count (done either by fdget() or by fork()).
+ */
+
+void set_close_on_exec(unsigned int fd, int flag)
+{
+	struct files_struct *files = current->files;
+	spin_lock(&files->file_lock);
+	__set_close_on_exec(fd, files_fdtable(files), flag);
+	spin_unlock(&files->file_lock);
+}
+
+bool get_close_on_exec(unsigned int fd)
+{
+	bool res;
+	rcu_read_lock();
+	res = close_on_exec(fd, current->files);
+	rcu_read_unlock();
+	return res;
+}
+
+static int do_dup2(struct files_struct *files,
+	struct file *file, unsigned fd, unsigned flags)
+__releases(&files->file_lock)
+{
+	struct file *tofree;
+	struct fdtable *fdt;
+
+	/*
+	 * dup2() is expected to close the file installed in the target fd slot
+	 * (if any). However, userspace hand-picking a fd may be racing against
+	 * its own threads which happened to allocate it in open() et al but did
+	 * not populate it yet.
+	 *
+	 * Broadly speaking we may be racing against the following:
+	 * fd = get_unused_fd_flags();     // fd slot reserved, ->fd[fd] == NULL
+	 * file = hard_work_goes_here();
+	 * fd_install(fd, file);           // only now ->fd[fd] == file
+	 *
+	 * It is an invariant that a successfully allocated fd has a NULL entry
+	 * in the array until the matching fd_install().
+	 *
+	 * If we fit the window, we have the fd to populate, yet no target file
+	 * to close. Trying to ignore it and install our new file would violate
+	 * the invariant and make fd_install() overwrite our file.
+	 *
+	 * Things can be done(tm) to handle this. However, the issue does not
+	 * concern legitimate programs and we only need to make sure the kernel
+	 * does not trip over it.
+	 *
+	 * The simplest way out is to return an error if we find ourselves here.
+	 *
+	 * POSIX is silent on the issue, we return -EBUSY.
+	 */
+	fdt = files_fdtable(files);
+	fd = array_index_nospec(fd, fdt->max_fds);
+	tofree = rcu_dereference_raw(fdt->fd[fd]);
+	if (!tofree && fd_is_open(fd, fdt))
+		goto Ebusy;
+	get_file(file);
+	rcu_assign_pointer(fdt->fd[fd], file);
+	__set_open_fd(fd, fdt, flags & O_CLOEXEC);
+	spin_unlock(&files->file_lock);
+
+	if (tofree)
+		filp_close(tofree, files);
+
+	return fd;
+
+Ebusy:
+	spin_unlock(&files->file_lock);
+	return -EBUSY;
+}
+
+int replace_fd(unsigned fd, struct file *file, unsigned flags)
+{
+	int err;
+	struct files_struct *files = current->files;
+
+	if (!file)
+		return close_fd(fd);
+
+	if (fd >= rlimit(RLIMIT_NOFILE))
+		return -EBADF;
+
+	spin_lock(&files->file_lock);
+	err = expand_files(files, fd);
+	if (unlikely(err < 0))
+		goto out_unlock;
+	err = do_dup2(files, file, fd, flags);
+	if (err < 0)
+		return err;
+	return 0;
+
+out_unlock:
+	spin_unlock(&files->file_lock);
+	return err;
+}
+
+/**
+ * receive_fd() - Install received file into file descriptor table
+ * @file: struct file that was received from another process
+ * @ufd: __user pointer to write new fd number to
+ * @o_flags: the O_* flags to apply to the new fd entry
+ *
+ * Installs a received file into the file descriptor table, with appropriate
+ * checks and count updates. Optionally writes the fd number to userspace, if
+ * @ufd is non-NULL.
+ *
+ * This helper handles its own reference counting of the incoming
+ * struct file.
+ *
+ * Returns newly install fd or -ve on error.
+ */
+int receive_fd(struct file *file, int __user *ufd, unsigned int o_flags)
+{
+	int error;
+
+	error = security_file_receive(file);
+	if (error)
+		return error;
+
+	FD_PREPARE(fdf, o_flags, file);
+	if (fdf.err)
+		return fdf.err;
+	get_file(file);
+
+	if (ufd) {
+		error = put_user(fd_prepare_fd(fdf), ufd);
+		if (error)
+			return error;
+	}
+
+	__receive_sock(fd_prepare_file(fdf));
+	return fd_publish(fdf);
+}
+EXPORT_SYMBOL_GPL(receive_fd);
+
+int receive_fd_replace(int new_fd, struct file *file, unsigned int o_flags)
+{
+	int error;
+
+	error = security_file_receive(file);
+	if (error)
+		return error;
+	error = replace_fd(new_fd, file, o_flags);
+	if (error)
+		return error;
+	__receive_sock(file);
+	return new_fd;
+}
+
+static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
+{
+	int err = -EBADF;
+	struct file *file;
+	struct files_struct *files = current->files;
+
+	if ((flags & ~O_CLOEXEC) != 0)
+		return -EINVAL;
+
+	if (unlikely(oldfd == newfd))
+		return -EINVAL;
+
+	if (newfd >= rlimit(RLIMIT_NOFILE))
+		return -EBADF;
+
+	spin_lock(&files->file_lock);
+	err = expand_files(files, newfd);
+	file = files_lookup_fd_locked(files, oldfd);
+	if (unlikely(!file))
+		goto Ebadf;
+	if (unlikely(err < 0)) {
+		if (err == -EMFILE)
+			goto Ebadf;
+		goto out_unlock;
+	}
+	return do_dup2(files, file, newfd, flags);
+
+Ebadf:
+	err = -EBADF;
+out_unlock:
+	spin_unlock(&files->file_lock);
+	return err;
+}
+
+SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
+{
+	return ksys_dup3(oldfd, newfd, flags);
+}
+
+SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
+{
+	if (unlikely(newfd == oldfd)) { /* corner case */
+		struct files_struct *files = current->files;
+		struct file *f;
+		int retval = oldfd;
+
+		rcu_read_lock();
+		f = __fget_files_rcu(files, oldfd, 0);
+		if (!f)
+			retval = -EBADF;
+		rcu_read_unlock();
+		if (f)
+			fput(f);
+		return retval;
+	}
+	return ksys_dup3(oldfd, newfd, 0);
+}
+
+SYSCALL_DEFINE1(dup, unsigned int, fildes)
+{
+	int ret = -EBADF;
+	struct file *file = fget_raw(fildes);
+
+	if (file) {
+		ret = get_unused_fd_flags(0);
+		if (ret >= 0)
+			fd_install(ret, file);
+		else
+			fput(file);
+	}
+	return ret;
+}
+
+int f_dupfd(unsigned int from, struct file *file, unsigned flags)
+{
+	unsigned long nofile = rlimit(RLIMIT_NOFILE);
+	int err;
+	if (from >= nofile)
+		return -EINVAL;
+	err = alloc_fd(from, nofile, flags);
+	if (err >= 0) {
+		get_file(file);
+		fd_install(err, file);
+	}
+	return err;
+}
+
+int iterate_fd(struct files_struct *files, unsigned n,
+		int (*f)(const void *, struct file *, unsigned),
+		const void *p)
+{
+	struct fdtable *fdt;
+	int res = 0;
+	if (!files)
+		return 0;
+	spin_lock(&files->file_lock);
+	for (fdt = files_fdtable(files); n < fdt->max_fds; n++) {
+		struct file *file;
+		file = rcu_dereference_check_fdtable(files, fdt->fd[n]);
+		if (!file)
+			continue;
+		res = f(p, file, n);
+		if (res)
+			break;
+	}
+	spin_unlock(&files->file_lock);
+	return res;
+}
+EXPORT_SYMBOL(iterate_fd);