Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 649 insertions, 0 deletions

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
new file mode 100644
index 000000000..844d65eb4
--- /dev/null
+++ b/Documentation/filesystems/locking.rst
@@ -0,0 +1,649 @@
+=======
+Locking
+=======
+
+The text below describes the locking rules for VFS-related methods.
+It is (believed to be) up-to-date. *Please*, if you change anything in
+prototypes or locking protocols - update this file. And update the relevant
+instances in the tree, don't leave that to maintainers of filesystems/devices/
+etc. At the very least, put the list of dubious cases in the end of this file.
+Don't turn it into log - maintainers of out-of-the-tree code are supposed to
+be able to use diff(1).
+
+Thing currently missing here: socket operations. Alexey?
+
+dentry_operations
+=================
+
+prototypes::
+
+	int (*d_revalidate)(struct inode *, const struct qstr *,
+			    struct dentry *, unsigned int);
+	int (*d_weak_revalidate)(struct dentry *, unsigned int);
+	int (*d_hash)(const struct dentry *, struct qstr *);
+	int (*d_compare)(const struct dentry *,
+			unsigned int, const char *, const struct qstr *);
+	int (*d_delete)(struct dentry *);
+	int (*d_init)(struct dentry *);
+	void (*d_release)(struct dentry *);
+	void (*d_iput)(struct dentry *, struct inode *);
+	char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
+	struct vfsmount *(*d_automount)(struct path *path);
+	int (*d_manage)(const struct path *, bool);
+	struct dentry *(*d_real)(struct dentry *, enum d_real_type type);
+	bool (*d_unalias_trylock)(const struct dentry *);
+	void (*d_unalias_unlock)(const struct dentry *);
+
+locking rules:
+
+================== ===========	========	==============	========
+ops		   rename_lock	->d_lock	may block	rcu-walk
+================== ===========	========	==============	========
+d_revalidate:	   no		no		yes (ref-walk)	maybe
+d_weak_revalidate: no		no		yes	 	no
+d_hash		   no		no		no		maybe
+d_compare:	   yes		no		no		maybe
+d_delete:	   no		yes		no		no
+d_init:		   no		no		yes		no
+d_release:	   no		no		yes		no
+d_prune:           no		yes		no		no
+d_iput:		   no		no		yes		no
+d_dname:	   no		no		no		no
+d_automount:	   no		no		yes		no
+d_manage:	   no		no		yes (ref-walk)	maybe
+d_real		   no		no		yes 		no
+d_unalias_trylock  yes		no		no 		no
+d_unalias_unlock   yes		no		no 		no
+================== ===========	========	==============	========
+
+inode_operations
+================
+
+prototypes::
+
+	int (*create) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t);
+	struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int);
+	int (*link) (struct dentry *,struct inode *,struct dentry *);
+	int (*unlink) (struct inode *,struct dentry *);
+	int (*symlink) (struct mnt_idmap *, struct inode *,struct dentry *,const char *);
+	struct dentry *(*mkdir) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t);
+	int (*rmdir) (struct inode *,struct dentry *);
+	int (*mknod) (struct mnt_idmap *, struct inode *,struct dentry *,umode_t,dev_t);
+	int (*rename) (struct mnt_idmap *, struct inode *, struct dentry *,
+			struct inode *, struct dentry *, unsigned int);
+	int (*readlink) (struct dentry *, char __user *,int);
+	const char *(*get_link) (struct dentry *, struct inode *, struct delayed_call *);
+	void (*truncate) (struct inode *);
+	int (*permission) (struct mnt_idmap *, struct inode *, int, unsigned int);
+	struct posix_acl * (*get_inode_acl)(struct inode *, int, bool);
+	int (*setattr) (struct mnt_idmap *, struct dentry *, struct iattr *);
+	int (*getattr) (struct mnt_idmap *, const struct path *, struct kstat *, u32, unsigned int);
+	ssize_t (*listxattr) (struct dentry *, char *, size_t);
+	int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
+	void (*update_time)(struct inode *inode, enum fs_update_time type,
+			    int flags);
+	void (*sync_lazytime)(struct inode *inode);
+	int (*atomic_open)(struct inode *, struct dentry *,
+				struct file *, unsigned open_flag,
+				umode_t create_mode);
+	int (*tmpfile) (struct mnt_idmap *, struct inode *,
+			struct file *, umode_t);
+	int (*fileattr_set)(struct mnt_idmap *idmap,
+			    struct dentry *dentry, struct file_kattr *fa);
+	int (*fileattr_get)(struct dentry *dentry, struct file_kattr *fa);
+	struct posix_acl * (*get_acl)(struct mnt_idmap *, struct dentry *, int);
+	struct offset_ctx *(*get_offset_ctx)(struct inode *inode);
+
+locking rules:
+	all may block
+
+==============	==================================================
+ops		i_rwsem(inode)
+==============	==================================================
+lookup:		shared
+create:		exclusive
+link:		exclusive (both)
+mknod:		exclusive
+symlink:	exclusive
+mkdir:		exclusive
+unlink:		exclusive (both)
+rmdir:		exclusive (both)(see below)
+rename:		exclusive (both parents, some children)	(see below)
+readlink:	no
+get_link:	no
+setattr:	exclusive
+permission:	no (may not block if called in rcu-walk mode)
+get_inode_acl:	no
+get_acl:	no
+getattr:	no
+listxattr:	no
+fiemap:		no
+update_time:	no
+sync_lazytime:	no
+atomic_open:	shared (exclusive if O_CREAT is set in open flags)
+tmpfile:	no
+fileattr_get:	no or exclusive
+fileattr_set:	exclusive
+get_offset_ctx  no
+==============	==================================================
+
+
+	Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_rwsem
+	exclusive on victim.
+	cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
+	->unlink() and ->rename() have ->i_rwsem exclusive on all non-directories
+	involved.
+	->rename() has ->i_rwsem exclusive on any subdirectory that changes parent.
+
+See Documentation/filesystems/directory-locking.rst for more detailed discussion
+of the locking scheme for directory operations.
+
+xattr_handler operations
+========================
+
+prototypes::
+
+	bool (*list)(struct dentry *dentry);
+	int (*get)(const struct xattr_handler *handler, struct dentry *dentry,
+		   struct inode *inode, const char *name, void *buffer,
+		   size_t size);
+	int (*set)(const struct xattr_handler *handler,
+                   struct mnt_idmap *idmap,
+                   struct dentry *dentry, struct inode *inode, const char *name,
+                   const void *buffer, size_t size, int flags);
+
+locking rules:
+	all may block
+
+=====		==============
+ops		i_rwsem(inode)
+=====		==============
+list:		no
+get:		no
+set:		exclusive
+=====		==============
+
+super_operations
+================
+
+prototypes::
+
+	struct inode *(*alloc_inode)(struct super_block *sb);
+	void (*free_inode)(struct inode *);
+	void (*destroy_inode)(struct inode *);
+	void (*dirty_inode) (struct inode *, int flags);
+	int (*write_inode) (struct inode *, struct writeback_control *wbc);
+	int (*drop_inode) (struct inode *);
+	void (*evict_inode) (struct inode *);
+	void (*put_super) (struct super_block *);
+	int (*sync_fs)(struct super_block *sb, int wait);
+	int (*freeze_fs) (struct super_block *);
+	int (*unfreeze_fs) (struct super_block *);
+	int (*statfs) (struct dentry *, struct kstatfs *);
+	void (*umount_begin) (struct super_block *);
+	int (*show_options)(struct seq_file *, struct dentry *);
+	ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
+	ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
+
+locking rules:
+	All may block [not true, see below]
+
+======================	============	========================
+ops			s_umount	note
+======================	============	========================
+alloc_inode:
+free_inode:				called from RCU callback
+destroy_inode:
+dirty_inode:
+write_inode:
+drop_inode:				!!!inode->i_lock!!!
+evict_inode:
+put_super:		write
+sync_fs:		read
+freeze_fs:		write
+unfreeze_fs:		write
+statfs:			maybe(read)	(see below)
+umount_begin:		no
+show_options:		no		(namespace_sem)
+quota_read:		no		(see below)
+quota_write:		no		(see below)
+======================	============	========================
+
+->statfs() has s_umount (shared) when called by ustat(2) (native or
+compat), but that's an accident of bad API; s_umount is used to pin
+the superblock down when we only have dev_t given us by userland to
+identify the superblock.  Everything else (statfs(), fstatfs(), etc.)
+doesn't hold it when calling ->statfs() - superblock is pinned down
+by resolving the pathname passed to syscall.
+
+->quota_read() and ->quota_write() functions are both guaranteed to
+be the only ones operating on the quota file by the quota code (via
+dqio_sem) (unless an admin really wants to screw up something and
+writes to quota files with quotas on). For other details about locking
+see also dquot_operations section.
+
+file_system_type
+================
+
+prototypes::
+
+	void (*kill_sb) (struct super_block *);
+
+locking rules:
+
+=======		=========
+ops		may block
+=======		=========
+kill_sb		yes
+=======		=========
+
+->kill_sb() takes a write-locked superblock, does all shutdown work on it,
+unlocks and drops the reference.
+
+address_space_operations
+========================
+prototypes::
+
+	int (*read_folio)(struct file *, struct folio *);
+	int (*writepages)(struct address_space *, struct writeback_control *);
+	bool (*dirty_folio)(struct address_space *, struct folio *folio);
+	void (*readahead)(struct readahead_control *);
+	int (*write_begin)(const struct kiocb *, struct address_space *mapping,
+				loff_t pos, unsigned len,
+				struct folio **foliop, void **fsdata);
+	int (*write_end)(const struct kiocb *, struct address_space *mapping,
+				loff_t pos, unsigned len, unsigned copied,
+				struct folio *folio, void *fsdata);
+	sector_t (*bmap)(struct address_space *, sector_t);
+	void (*invalidate_folio) (struct folio *, size_t start, size_t len);
+	bool (*release_folio)(struct folio *, gfp_t);
+	void (*free_folio)(struct folio *);
+	int (*direct_IO)(struct kiocb *, struct iov_iter *iter);
+	int (*migrate_folio)(struct address_space *, struct folio *dst,
+			struct folio *src, enum migrate_mode);
+	int (*launder_folio)(struct folio *);
+	bool (*is_partially_uptodate)(struct folio *, size_t from, size_t count);
+	int (*error_remove_folio)(struct address_space *, struct folio *);
+	int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span)
+	int (*swap_deactivate)(struct file *);
+
+locking rules:
+	All except dirty_folio and free_folio may block
+
+======================	======================== =========	===============
+ops			folio locked		 i_rwsem	invalidate_lock
+======================	======================== =========	===============
+read_folio:		yes, unlocks				shared
+writepages:
+dirty_folio:		maybe
+readahead:		yes, unlocks				shared
+write_begin:		locks the folio		 exclusive
+write_end:		yes, unlocks		 exclusive
+bmap:
+invalidate_folio:	yes					exclusive
+release_folio:		yes
+free_folio:		yes
+direct_IO:
+migrate_folio:		yes (both)
+launder_folio:		yes
+is_partially_uptodate:	yes
+error_remove_folio:	yes
+swap_activate:		no
+swap_deactivate:	no
+======================	======================== =========	===============
+
+->write_begin(), ->write_end() and ->read_folio() may be called from
+the request handler (/dev/loop).
+
+->read_folio() unlocks the folio, either synchronously or via I/O
+completion.
+
+->readahead() unlocks the folios that I/O is attempted on like ->read_folio().
+
+->writepages() is used for periodic writeback and for syscall-initiated
+sync operations.  The address_space should start I/O against at least
+``*nr_to_write`` pages.  ``*nr_to_write`` must be decremented for each page
+which is written.  The address_space implementation may write more (or less)
+pages than ``*nr_to_write`` asks for, but it should try to be reasonably close.
+If nr_to_write is NULL, all dirty pages must be written.
+
+writepages should _only_ write pages which are present in
+mapping->i_pages.
+
+->dirty_folio() is called from various places in the kernel when
+the target folio is marked as needing writeback.  The folio cannot be
+truncated because either the caller holds the folio lock, or the caller
+has found the folio while holding the page table lock which will block
+truncation.
+
+->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
+filesystems and by the swapper. The latter will eventually go away.  Please,
+keep it that way and don't breed new callers.
+
+->invalidate_folio() is called when the filesystem must attempt to drop
+some or all of the buffers from the page when it is being truncated. It
+returns zero on success.  The filesystem must exclusively acquire
+invalidate_lock before invalidating page cache in truncate / hole punch
+path (and thus calling into ->invalidate_folio) to block races between page
+cache invalidation and page cache filling functions (fault, read, ...).
+
+->release_folio() is called when the MM wants to make a change to the
+folio that would invalidate the filesystem's private data.  For example,
+it may be about to be removed from the address_space or split.  The folio
+is locked and not under writeback.  It may be dirty.  The gfp parameter
+is not usually used for allocation, but rather to indicate what the
+filesystem may do to attempt to free the private data.  The filesystem may
+return false to indicate that the folio's private data cannot be freed.
+If it returns true, it should have already removed the private data from
+the folio.  If a filesystem does not provide a ->release_folio method,
+the pagecache will assume that private data is buffer_heads and call
+try_to_free_buffers().
+
+->free_folio() is called when the kernel has dropped the folio
+from the page cache.
+
+->launder_folio() may be called prior to releasing a folio if
+it is still found to be dirty. It returns zero if the folio was successfully
+cleaned, or an error value if not. Note that in order to prevent the folio
+getting mapped back in and redirtied, it needs to be kept locked
+across the entire operation.
+
+->swap_activate() will be called to prepare the given file for swap.  It
+should perform any validation and preparation necessary to ensure that
+writes can be performed with minimal memory allocation.  It should call
+add_swap_extent(), or the helper iomap_swapfile_activate(), and return
+the number of extents added.  If IO should be submitted through
+the file system it should call swap_fs_activate, otherwise IO will be
+submitted directly to the block device ``sis->bdev``.
+
+->swap_deactivate() will be called in the sys_swapoff()
+path after ->swap_activate() returned success.
+
+file_lock_operations
+====================
+
+prototypes::
+
+	void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
+	void (*fl_release_private)(struct file_lock *);
+
+
+locking rules:
+
+===================	=============	=========
+ops			inode->i_lock	may block
+===================	=============	=========
+fl_copy_lock:		yes		no
+fl_release_private:	maybe		maybe[1]_
+===================	=============	=========
+
+.. [1]:
+   ->fl_release_private for flock or POSIX locks is currently allowed
+   to block. Leases however can still be freed while the i_lock is held and
+   so fl_release_private called on a lease should not block.
+
+lock_manager_operations
+=======================
+
+prototypes::
+
+	void (*lm_notify)(struct file_lock *);  /* unblock callback */
+	int (*lm_grant)(struct file_lock *, struct file_lock *, int);
+	void (*lm_break)(struct file_lock *); /* break_lease callback */
+	int (*lm_change)(struct file_lock **, int);
+	bool (*lm_breaker_owns_lease)(struct file_lock *);
+        bool (*lm_lock_expirable)(struct file_lock *);
+        void (*lm_expire_lock)(void);
+        bool (*lm_breaker_timedout)(struct file_lease *);
+
+locking rules:
+
+======================	=============	=================	=========
+ops			   flc_lock  	blocked_lock_lock	may block
+======================	=============	=================	=========
+lm_notify:		no      	yes			no
+lm_grant:		no		no			no
+lm_break:		yes		no			no
+lm_change		yes		no			no
+lm_breaker_owns_lease:	yes     	no			no
+lm_lock_expirable	yes		no			no
+lm_expire_lock		no		no			yes
+lm_open_conflict	yes		no			no
+lm_breaker_timedout     yes             no                      no
+======================	=============	=================	=========
+
+block_device_operations
+=======================
+prototypes::
+
+	int (*open) (struct block_device *, fmode_t);
+	int (*release) (struct gendisk *, fmode_t);
+	int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
+	int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
+	int (*direct_access) (struct block_device *, sector_t, void **,
+				unsigned long *);
+	void (*unlock_native_capacity) (struct gendisk *);
+	int (*getgeo)(struct gendisk *, struct hd_geometry *);
+	void (*swap_slot_free_notify) (struct block_device *, unsigned long);
+
+locking rules:
+
+======================= ===================
+ops			open_mutex
+======================= ===================
+open:			yes
+release:		yes
+ioctl:			no
+compat_ioctl:		no
+direct_access:		no
+unlock_native_capacity:	no
+getgeo:			no
+swap_slot_free_notify:	no	(see below)
+======================= ===================
+
+swap_slot_free_notify is called with swap_lock and sometimes the page lock
+held.
+
+
+file_operations
+===============
+
+prototypes::
+
+	loff_t (*llseek) (struct file *, loff_t, int);
+	ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
+	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
+	ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
+	ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
+	int (*iopoll) (struct kiocb *kiocb, bool spin);
+	int (*iterate_shared) (struct file *, struct dir_context *);
+	__poll_t (*poll) (struct file *, struct poll_table_struct *);
+	long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
+	long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
+	int (*mmap) (struct file *, struct vm_area_struct *);
+	int (*open) (struct inode *, struct file *);
+	int (*flush) (struct file *);
+	int (*release) (struct inode *, struct file *);
+	int (*fsync) (struct file *, loff_t start, loff_t end, int datasync);
+	int (*fasync) (int, struct file *, int);
+	int (*lock) (struct file *, int, struct file_lock *);
+	unsigned long (*get_unmapped_area)(struct file *, unsigned long,
+			unsigned long, unsigned long, unsigned long);
+	int (*check_flags)(int);
+	int (*flock) (struct file *, int, struct file_lock *);
+	ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
+			size_t, unsigned int);
+	ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
+			size_t, unsigned int);
+	int (*setlease)(struct file *, long, struct file_lock **, void **);
+	long (*fallocate)(struct file *, int, loff_t, loff_t);
+	void (*show_fdinfo)(struct seq_file *m, struct file *f);
+	unsigned (*mmap_capabilities)(struct file *);
+	ssize_t (*copy_file_range)(struct file *, loff_t, struct file *,
+			loff_t, size_t, unsigned int);
+	loff_t (*remap_file_range)(struct file *file_in, loff_t pos_in,
+			struct file *file_out, loff_t pos_out,
+			loff_t len, unsigned int remap_flags);
+	int (*fadvise)(struct file *, loff_t, loff_t, int);
+
+locking rules:
+	All may block.
+
+->llseek() locking has moved from llseek to the individual llseek
+implementations.  If your fs is not using generic_file_llseek, you
+need to acquire and release the appropriate locks in your ->llseek().
+For many filesystems, it is probably safe to acquire the inode
+mutex or just to use i_size_read() instead.
+Note: this does not protect the file->f_pos against concurrent modifications
+since this is something the userspace has to take care about.
+
+->iterate_shared() is called with i_rwsem held for reading, and with the
+file f_pos_lock held exclusively
+
+->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
+Most instances call fasync_helper(), which does that maintenance, so it's
+not normally something one needs to worry about.  Return values > 0 will be
+mapped to zero in the VFS layer.
+
+->readdir() and ->ioctl() on directories must be changed. Ideally we would
+move ->readdir() to inode_operations and use a separate method for directory
+->ioctl() or kill the latter completely. One of the problems is that for
+anything that resembles union-mount we won't have a struct file for all
+components. And there are other reasons why the current interface is a mess...
+
+->read on directories probably must go away - we should just enforce -EISDIR
+in sys_read() and friends.
+
+->setlease operations should call generic_setlease() before or after setting
+the lease within the individual filesystem to record the result of the
+operation
+
+->fallocate implementation must be really careful to maintain page cache
+consistency when punching holes or performing other operations that invalidate
+page cache contents. Usually the filesystem needs to call
+truncate_inode_pages_range() to invalidate relevant range of the page cache.
+However the filesystem usually also needs to update its internal (and on disk)
+view of file offset -> disk block mapping. Until this update is finished, the
+filesystem needs to block page faults and reads from reloading now-stale page
+cache contents from the disk. Since VFS acquires mapping->invalidate_lock in
+shared mode when loading pages from disk (filemap_fault(), filemap_read(),
+readahead paths), the fallocate implementation must take the invalidate_lock to
+prevent reloading.
+
+->copy_file_range and ->remap_file_range implementations need to serialize
+against modifications of file data while the operation is running. For
+blocking changes through write(2) and similar operations inode->i_rwsem can be
+used. To block changes to file contents via a memory mapping during the
+operation, the filesystem must take mapping->invalidate_lock to coordinate
+with ->page_mkwrite.
+
+dquot_operations
+================
+
+prototypes::
+
+	int (*write_dquot) (struct dquot *);
+	int (*acquire_dquot) (struct dquot *);
+	int (*release_dquot) (struct dquot *);
+	int (*mark_dirty) (struct dquot *);
+	int (*write_info) (struct super_block *, int);
+
+These operations are intended to be more or less wrapping functions that ensure
+a proper locking wrt the filesystem and call the generic quota operations.
+
+What filesystem should expect from the generic quota functions:
+
+==============	============	=========================
+ops		FS recursion	Held locks when called
+==============	============	=========================
+write_dquot:	yes		dqonoff_sem or dqptr_sem
+acquire_dquot:	yes		dqonoff_sem or dqptr_sem
+release_dquot:	yes		dqonoff_sem or dqptr_sem
+mark_dirty:	no		-
+write_info:	yes		dqonoff_sem
+==============	============	=========================
+
+FS recursion means calling ->quota_read() and ->quota_write() from superblock
+operations.
+
+More details about quota locking can be found in fs/quota/dquot.c.
+
+vm_operations_struct
+====================
+
+prototypes::
+
+	void (*open)(struct vm_area_struct *);
+	void (*close)(struct vm_area_struct *);
+	vm_fault_t (*fault)(struct vm_fault *);
+	vm_fault_t (*huge_fault)(struct vm_fault *, unsigned int order);
+	vm_fault_t (*map_pages)(struct vm_fault *, pgoff_t start, pgoff_t end);
+	vm_fault_t (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
+	vm_fault_t (*pfn_mkwrite)(struct vm_area_struct *, struct vm_fault *);
+	int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
+
+locking rules:
+
+=============	==========	===========================
+ops		mmap_lock	PageLocked(page)
+=============	==========	===========================
+open:		write
+close:		read/write
+fault:		read		can return with page locked
+huge_fault:	maybe-read
+map_pages:	maybe-read
+page_mkwrite:	read		can return with page locked
+pfn_mkwrite:	read
+access:		read
+=============	==========	===========================
+
+->fault() is called when a previously not present pte is about to be faulted
+in. The filesystem must find and return the page associated with the passed in
+"pgoff" in the vm_fault structure. If it is possible that the page may be
+truncated and/or invalidated, then the filesystem must lock invalidate_lock,
+then ensure the page is not already truncated (invalidate_lock will block
+subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
+locked. The VM will unlock the page.
+
+->huge_fault() is called when there is no PUD or PMD entry present.  This
+gives the filesystem the opportunity to install a PUD or PMD sized page.
+Filesystems can also use the ->fault method to return a PMD sized page,
+so implementing this function may not be necessary.  In particular,
+filesystems should not call filemap_fault() from ->huge_fault().
+The mmap_lock may not be held when this method is called.
+
+->map_pages() is called when VM asks to map easy accessible pages.
+Filesystem should find and map pages associated with offsets from "start_pgoff"
+till "end_pgoff". ->map_pages() is called with the RCU lock held and must
+not block.  If it's not possible to reach a page without blocking,
+filesystem should skip it. Filesystem should use set_pte_range() to setup
+page table entry. Pointer to entry associated with the page is passed in
+"pte" field in vm_fault structure. Pointers to entries for other offsets
+should be calculated relative to "pte".
+
+->page_mkwrite() is called when a previously read-only pte is about to become
+writeable. The filesystem again must ensure that there are no
+truncate/invalidate races or races with operations such as ->remap_file_range
+or ->copy_file_range, and then return with the page locked. Usually
+mapping->invalidate_lock is suitable for proper serialization. If the page has
+been truncated, the filesystem should not look up a new page like the ->fault()
+handler, but simply return with VM_FAULT_NOPAGE, which will cause the VM to
+retry the fault.
+
+->pfn_mkwrite() is the same as page_mkwrite but when the pte is
+VM_PFNMAP or VM_MIXEDMAP with a page-less entry. Expected return is
+VM_FAULT_NOPAGE. Or one of the VM_FAULT_ERROR types. The default behavior
+after this call is to make the pte read-write, unless pfn_mkwrite returns
+an error.
+
+->access() is called when get_user_pages() fails in
+access_process_vm(), typically used to debug a process through
+/proc/pid/mem or ptrace.  This function is needed only for
+VM_IO | VM_PFNMAP VMAs.
+
+--------------------------------------------------------------------------------
+
+			Dubious stuff
+
+(if you break something or notice that it is broken and do not fix it yourself
+- at least put it here)