From 034dd340b08be1f2f0477ad16131d609f9dbd53c Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 30 Aug 2026 09:22:00 -0700 Subject: Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace 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 --- lib/errseq.c | 208 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 208 insertions(+) create mode 100644 lib/errseq.c (limited to 'lib/errseq.c') diff --git a/lib/errseq.c b/lib/errseq.c new file mode 100644 index 000000000..13a2581c5 --- /dev/null +++ b/lib/errseq.c @@ -0,0 +1,208 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include +#include + +/* + * An errseq_t is a way of recording errors in one place, and allowing any + * number of "subscribers" to tell whether it has changed since a previous + * point where it was sampled. + * + * It's implemented as an unsigned 32-bit value. The low order bits are + * designated to hold an error code (between 0 and -MAX_ERRNO). The upper bits + * are used as a counter. This is done with atomics instead of locking so that + * these functions can be called from any context. + * + * The general idea is for consumers to sample an errseq_t value. That value + * can later be used to tell whether any new errors have occurred since that + * sampling was done. + * + * Note that there is a risk of collisions if new errors are being recorded + * frequently, since we have so few bits to use as a counter. + * + * To mitigate this, one bit is used as a flag to tell whether the value has + * been sampled since a new value was recorded. That allows us to avoid bumping + * the counter if no one has sampled it since the last time an error was + * recorded. + * + * A new errseq_t should always be zeroed out. A errseq_t value of all zeroes + * is the special (but common) case where there has never been an error. An all + * zero value thus serves as the "epoch" if one wishes to know whether there + * has ever been an error set since it was first initialized. + */ + +/* The low bits are designated for error code (max of MAX_ERRNO) */ +#define ERRSEQ_SHIFT (ilog2(MAX_ERRNO) + 1) + +/* This bit is used as a flag to indicate whether the value has been seen */ +#define ERRSEQ_SEEN (1 << ERRSEQ_SHIFT) + +/* Leverage macro ERRSEQ_SEEN to define errno mask macro here */ +#define ERRNO_MASK (ERRSEQ_SEEN - 1) + +/* The lowest bit of the counter */ +#define ERRSEQ_CTR_INC (1 << (ERRSEQ_SHIFT + 1)) + +/** + * errseq_set - set a errseq_t for later reporting + * @eseq: errseq_t field that should be set + * @err: error to set (must be between -1 and -MAX_ERRNO) + * + * This function sets the error in @eseq, and increments the sequence counter + * if the last sequence was sampled at some point in the past. + * + * Any error set will always overwrite an existing error. + * + * Return: The previous value, primarily for debugging purposes. The + * return value should not be used as a previously sampled value in later + * calls as it will not have the SEEN flag set. + */ +errseq_t errseq_set(errseq_t *eseq, int err) +{ + errseq_t cur, old; + + + /* + * Ensure the error code actually fits where we want it to go. If it + * doesn't then just throw a warning and don't record anything. We + * also don't accept zero here as that would effectively clear a + * previous error. + */ + old = READ_ONCE(*eseq); + + if (WARN(unlikely(err == 0 || (unsigned int)-err > MAX_ERRNO), + "err = %d\n", err)) + return old; + + for (;;) { + errseq_t new; + + /* Clear out error bits and set new error */ + new = (old & ~(ERRNO_MASK | ERRSEQ_SEEN)) | -err; + + /* Only increment if someone has looked at it */ + if (old & ERRSEQ_SEEN) + new += ERRSEQ_CTR_INC; + + /* If there would be no change, then call it done */ + if (new == old) { + cur = new; + break; + } + + /* Try to swap the new value into place */ + cur = cmpxchg(eseq, old, new); + + /* + * Call it success if we did the swap or someone else beat us + * to it for the same value. + */ + if (likely(cur == old || cur == new)) + break; + + /* Raced with an update, try again */ + old = cur; + } + return cur; +} +EXPORT_SYMBOL(errseq_set); + +/** + * errseq_sample() - Grab current errseq_t value. + * @eseq: Pointer to errseq_t to be sampled. + * + * This function allows callers to initialise their errseq_t variable. + * If the error has been "seen", new callers will not see an old error. + * If there is an unseen error in @eseq, the caller of this function will + * see it the next time it checks for an error. + * + * Context: Any context. + * Return: The current errseq value. + */ +errseq_t errseq_sample(errseq_t *eseq) +{ + errseq_t old = READ_ONCE(*eseq); + + /* If nobody has seen this error yet, then we can be the first. */ + if (!(old & ERRSEQ_SEEN)) + old = 0; + return old; +} +EXPORT_SYMBOL(errseq_sample); + +/** + * errseq_check() - Has an error occurred since a particular sample point? + * @eseq: Pointer to errseq_t value to be checked. + * @since: Previously-sampled errseq_t from which to check. + * + * Grab the value that eseq points to, and see if it has changed @since + * the given value was sampled. The @since value is not advanced, so there + * is no need to mark the value as seen. + * + * Return: The latest error set in the errseq_t or 0 if it hasn't changed. + */ +int errseq_check(errseq_t *eseq, errseq_t since) +{ + errseq_t cur = READ_ONCE(*eseq); + + if (likely(cur == since)) + return 0; + return -(cur & ERRNO_MASK); +} +EXPORT_SYMBOL(errseq_check); + +/** + * errseq_check_and_advance() - Check an errseq_t and advance to current value. + * @eseq: Pointer to value being checked and reported. + * @since: Pointer to previously-sampled errseq_t to check against and advance. + * + * Grab the eseq value, and see whether it matches the value that @since + * points to. If it does, then just return 0. + * + * If it doesn't, then the value has changed. Set the "seen" flag, and try to + * swap it into place as the new eseq value. Then, set that value as the new + * "since" value, and return whatever the error portion is set to. + * + * Note that no locking is provided here for concurrent updates to the "since" + * value. The caller must provide that if necessary. Because of this, callers + * may want to do a lockless errseq_check before taking the lock and calling + * this. + * + * Return: Negative errno if one has been stored, or 0 if no new error has + * occurred. + */ +int errseq_check_and_advance(errseq_t *eseq, errseq_t *since) +{ + int err = 0; + errseq_t old, new; + + /* + * Most callers will want to use the inline wrapper to check this, + * so that the common case of no error is handled without needing + * to take the lock that protects the "since" value. + */ + old = READ_ONCE(*eseq); + if (old != *since) { + /* + * Set the flag and try to swap it into place if it has + * changed. + * + * We don't care about the outcome of the swap here. If the + * swap doesn't occur, then it has either been updated by a + * writer who is altering the value in some way (updating + * counter or resetting the error), or another reader who is + * just setting the "seen" flag. Either outcome is OK, and we + * can advance "since" and return an error based on what we + * have. + */ + new = old | ERRSEQ_SEEN; + if (new != old) + cmpxchg(eseq, old, new); + *since = new; + err = -(new & ERRNO_MASK); + } + return err; +} +EXPORT_SYMBOL(errseq_check_and_advance); -- cgit v1.3.1