Steven Rostedt (Google) 79b9e34b27 tracing/ring-buffer: Fix wait_on_pipe() race ... [ Upstream commit 2aa043a55b ] When the trace_pipe_raw file is closed, there should be no new readers on the file descriptor. This is mostly handled with the waking and wait_index fields of the iterator. But there's still a slight race. CPU 0 CPU 1 ----- ----- wait_index++; index = wait_index; ring_buffer_wake_waiters(); wait_on_pipe() ring_buffer_wait(); The ring_buffer_wait() will miss the wakeup from CPU 1. The problem is that the ring_buffer_wait() needs the logic of: prepare_to_wait(); if (!condition) schedule(); Where the missing condition check is the iter->wait_index update. Have the ring_buffer_wait() take a conditional callback function and a data parameter that can be used within the wait_event_interruptible() of the ring_buffer_wait() function. In wait_on_pipe(), pass a condition function that will check if the wait_index has been updated, if it has, it will return true to break out of the wait_event_interruptible() loop. Create a new field "closed" in the trace_iterator and set it in the .flush() callback before calling ring_buffer_wake_waiters(). This will keep any new readers from waiting on a closed file descriptor. Have the wait_on_pipe() condition callback also check the closed field. Change the wait_index field of the trace_iterator to atomic_t. There's no reason it needs to be 'long' and making it atomic and using atomic_read_acquire() and atomic_fetch_inc_release() will provide the necessary memory barriers. Add a "woken" flag to tracing_buffers_splice_read() to exit the loop after one more try to fetch data. That is, if it waited for data and something woke it up, it should try to collect any new data and then exit back to user space. Link: https://lore.kernel.org/linux-trace-kernel/CAHk-=wgsNgewHFxZAJiAQznwPMqEtQmi1waeS2O1v6L4c_Um5A@mail.gmail.com/ Link: https://lore.kernel.org/linux-trace-kernel/20240312121703.557950713@goodmis.org Cc: stable@vger.kernel.org Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: linke li <lilinke99@qq.com> Cc: Rabin Vincent <rabin@rab.in> Fixes: f3ddb74ad0 ("tracing: Wake up ring buffer waiters on closing of the file") Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> Signed-off-by: Sasha Levin <sashal@kernel.org>		2024-04-03 15:32:20 +02:00
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acpi	IOMMU Updates for Linux v6.8	2024-01-18 15:16:57 -08:00
asm-generic	RISC-V Patches for the 6.8 Merge Window, Part 4	2024-01-20 11:06:04 -08:00
clocksource
crypto
drm	drm: Fix drm_fixp2int_round() making it add 0.5	2024-03-26 18:17:35 -04:00
dt-bindings	clk: renesas: r8a779g0: Correct PFC/GPIO parent clocks	2024-03-26 18:17:05 -04:00
keys
kunit
kvm
linux	tracing/ring-buffer: Fix wait_on_pipe() race	2024-04-03 15:32:20 +02:00
math-emu
media	media: mc: Add num_links flag to media_pad	2024-04-03 15:32:03 +02:00
memory
misc
net	mac802154: fix llsec key resources release in mac802154_llsec_key_del	2024-04-03 15:32:15 +02:00
pcmcia
ras
rdma
rv
scsi	scsi: core: Consult supported VPD page list prior to fetching page	2024-02-15 14:41:26 -05:00
soc	soc: qcom: socinfo: rename PM2250 to PM4125	2024-03-26 18:16:34 -04:00
sound	ASoC: soc-card: Fix missing locking in snd_soc_card_get_kcontrol()	2024-02-23 13:40:06 +00:00
target
trace	tracing/net_sched: Fix tracepoints that save qdisc_dev() as a string	2024-03-04 09:35:54 +00:00
uapi	virtio: uapi: Drop __packed attribute in linux/virtio_pci.h	2024-03-26 18:17:35 -04:00
ufs
vdso
video
xen