linux-stable.git/kernel/events/ring_buffer.c, branch linux-5.4.y

perf/ring_buffer: Allow the EPOLLRDNORM flag for poll

2025-04-10T12:29:40+00:00

[ Upstream commit c96fff391c095c11dc87dab35be72dee7d217cde ]

The poll man page says POLLRDNORM is equivalent to POLLIN. For poll(),
it seems that if user sets pollfd with POLLRDNORM in userspace, perf_poll
will not return until timeout even if perf_output_wakeup called,
whereas POLLIN returns.

Fixes: 76369139ceb9 ("perf: Split up buffer handling from core code")
Signed-off-by: Tao Chen 
Signed-off-by: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: Arnaldo Carvalho de Melo 
Cc: "H. Peter Anvin" 
Cc: Linus Torvalds 
Link: https://lore.kernel.org/r/20250314030036.2543180-1-chen.dylane@linux.dev
Signed-off-by: Sasha Levin

perf/core: Add a new read format to get a number of lost samples

2023-12-13T17:18:15+00:00

[ Upstream commit 119a784c81270eb88e573174ed2209225d646656 ]

Sometimes we want to know an accurate number of samples even if it's
lost.  Currenlty PERF_RECORD_LOST is generated for a ring-buffer which
might be shared with other events.  So it's hard to know per-event
lost count.

Add event->lost_samples field and PERF_FORMAT_LOST to retrieve it from
userspace.

Original-patch-by: Jiri Olsa 
Signed-off-by: Namhyung Kim 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20220616180623.1358843-1-namhyung@kernel.org
Stable-dep-of: 382c27f4ed28 ("perf: Fix perf_event_validate_size()")
Signed-off-by: Sasha Levin

perf/core: Bail out early if the request AUX area is out of bound

2023-11-28T16:50:13+00:00

[ Upstream commit 54aee5f15b83437f23b2b2469bcf21bdd9823916 ]

When perf-record with a large AUX area, e.g 4GB, it fails with:

    #perf record -C 0 -m ,4G -e arm_spe_0// -- sleep 1
    failed to mmap with 12 (Cannot allocate memory)

and it reveals a WARNING with __alloc_pages():

	------------[ cut here ]------------
	WARNING: CPU: 44 PID: 17573 at mm/page_alloc.c:5568 __alloc_pages+0x1ec/0x248
	Call trace:
	 __alloc_pages+0x1ec/0x248
	 __kmalloc_large_node+0xc0/0x1f8
	 __kmalloc_node+0x134/0x1e8
	 rb_alloc_aux+0xe0/0x298
	 perf_mmap+0x440/0x660
	 mmap_region+0x308/0x8a8
	 do_mmap+0x3c0/0x528
	 vm_mmap_pgoff+0xf4/0x1b8
	 ksys_mmap_pgoff+0x18c/0x218
	 __arm64_sys_mmap+0x38/0x58
	 invoke_syscall+0x50/0x128
	 el0_svc_common.constprop.0+0x58/0x188
	 do_el0_svc+0x34/0x50
	 el0_svc+0x34/0x108
	 el0t_64_sync_handler+0xb8/0xc0
	 el0t_64_sync+0x1a4/0x1a8

'rb->aux_pages' allocated by kcalloc() is a pointer array which is used to
maintains AUX trace pages. The allocated page for this array is physically
contiguous (and virtually contiguous) with an order of 0..MAX_ORDER. If the
size of pointer array crosses the limitation set by MAX_ORDER, it reveals a
WARNING.

So bail out early with -ENOMEM if the request AUX area is out of bound,
e.g.:

    #perf record -C 0 -m ,4G -e arm_spe_0// -- sleep 1
    failed to mmap with 12 (Cannot allocate memory)

Signed-off-by: Shuai Xue 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Signed-off-by: Sasha Levin

perf/ring-buffer: Use regular variables for nesting

2019-05-24T07:00:11+00:00

While the IRQ/NMI will nest, the nest-count will be invariant over the
actual exception, since it will decrement equal to increment.

This means we can -- carefully -- use a regular variable since the
typical LOAD-STORE race doesn't exist (similar to preempt_count).

This optimizes the ring-buffer for all LOAD-STORE architectures, since
they need to use atomic ops to implement local_t.

Suggested-by: Alexander Shishkin 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Arnaldo Carvalho de Melo 
Cc: Jiri Olsa 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Stephane Eranian 
Cc: Thomas Gleixner 
Cc: Vince Weaver 
Cc: acme@kernel.org
Cc: mark.rutland@arm.com
Cc: namhyung@kernel.org
Cc: yabinc@google.com
Link: http://lkml.kernel.org/r/20190517115418.481392777@infradead.org
Signed-off-by: Ingo Molnar

perf/ring-buffer: Always use {READ,WRITE}_ONCE() for rb->user_page data

2019-05-24T07:00:11+00:00

We must use {READ,WRITE}_ONCE() on rb->user_page data such that
concurrent usage will see whole values. A few key sites were missing
this.

Suggested-by: Yabin Cui 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Alexander Shishkin 
Cc: Arnaldo Carvalho de Melo 
Cc: Jiri Olsa 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Stephane Eranian 
Cc: Thomas Gleixner 
Cc: Vince Weaver 
Cc: acme@kernel.org
Cc: mark.rutland@arm.com
Cc: namhyung@kernel.org
Fixes: 7b732a750477 ("perf_counter: new output ABI - part 1")
Link: http://lkml.kernel.org/r/20190517115418.394192145@infradead.org
Signed-off-by: Ingo Molnar

perf/ring_buffer: Add ordering to rb->nest increment

2019-05-24T07:00:10+00:00

Similar to how decrementing rb->next too early can cause data_head to
(temporarily) be observed to go backward, so too can this happen when
we increment too late.

This barrier() ensures the rb->head load happens after the increment,
both the one in the 'goto again' path, as the one from
perf_output_get_handle() -- albeit very unlikely to matter for the
latter.

Suggested-by: Yabin Cui 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Alexander Shishkin 
Cc: Arnaldo Carvalho de Melo 
Cc: Jiri Olsa 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Stephane Eranian 
Cc: Thomas Gleixner 
Cc: Vince Weaver 
Cc: acme@kernel.org
Cc: mark.rutland@arm.com
Cc: namhyung@kernel.org
Fixes: ef60777c9abd ("perf: Optimize the perf_output() path by removing IRQ-disables")
Link: http://lkml.kernel.org/r/20190517115418.309516009@infradead.org
Signed-off-by: Ingo Molnar

perf/ring_buffer: Fix exposing a temporarily decreased data_head

2019-05-24T07:00:10+00:00

In perf_output_put_handle(), an IRQ/NMI can happen in below location and
write records to the same ring buffer:

	...
	local_dec_and_test(&rb->nest)
	...                          <-- an IRQ/NMI can happen here
	rb->user_page->data_head = head;
	...

In this case, a value A is written to data_head in the IRQ, then a value
B is written to data_head after the IRQ. And A > B. As a result,
data_head is temporarily decreased from A to B. And a reader may see
data_head < data_tail if it read the buffer frequently enough, which
creates unexpected behaviors.

This can be fixed by moving dec(&rb->nest) to after updating data_head,
which prevents the IRQ/NMI above from updating data_head.

[ Split up by peterz. ]

Signed-off-by: Yabin Cui 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Alexander Shishkin 
Cc: Arnaldo Carvalho de Melo 
Cc: Arnaldo Carvalho de Melo 
Cc: Jiri Olsa 
Cc: Linus Torvalds 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Stephane Eranian 
Cc: Thomas Gleixner 
Cc: Vince Weaver 
Cc: mark.rutland@arm.com
Fixes: ef60777c9abd ("perf: Optimize the perf_output() path by removing IRQ-disables")
Link: http://lkml.kernel.org/r/20190517115418.224478157@infradead.org
Signed-off-by: Ingo Molnar

perf/ring_buffer: Fix AUX software double buffering

2019-05-03T10:46:10+00:00

This recent commit:

  5768402fd9c6e87 ("perf/ring_buffer: Use high order allocations for AUX buffers optimistically")

overlooked the fact that the previous one page granularity of the AUX buffer
provided an implicit double buffering capability to the PMU driver, which
went away when the entire buffer became one high-order page.

Always make the full-trace mode AUX allocation at least two-part to preserve
the previous behavior and allow the implicit double buffering to continue.

Reported-by: Ammy Yi 
Signed-off-by: Alexander Shishkin 
Acked-by: Peter Zijlstra 
Cc: Arnaldo Carvalho de Melo 
Cc: Jiri Olsa 
Cc: Linus Torvalds 
Cc: Stephane Eranian 
Cc: Thomas Gleixner 
Cc: Vince Weaver 
Cc: adrian.hunter@intel.com
Fixes: 5768402fd9c6e87 ("perf/ring_buffer: Use high order allocations for AUX buffers optimistically")
Link: http://lkml.kernel.org/r/20190503085536.24119-2-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar

perf/ring_buffer: Fix AUX record suppression

2019-04-16T10:13:57+00:00

The following commit:

  1627314fb54a33e ("perf: Suppress AUX/OVERWRITE records")

has an unintended side-effect of also suppressing all AUX records with no flags
and non-zero size, so all the regular records in the full trace mode.
This breaks some use cases for people.

Fix this by restoring "regular" AUX records.

Reported-by: Ben Gainey 
Tested-by: Ben Gainey 
Signed-off-by: Alexander Shishkin 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: 
Cc: Arnaldo Carvalho de Melo 
Cc: Jiri Olsa 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Stephane Eranian 
Cc: Thomas Gleixner 
Cc: Vince Weaver 
Fixes: 1627314fb54a33e ("perf: Suppress AUX/OVERWRITE records")
Link: https://lkml.kernel.org/r/20190329091338.29999-1-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar

perf/core: Fix perf_event_disable_inatomic() race

2019-04-12T06:55:55+00:00

Thomas-Mich Richter reported he triggered a WARN()ing from event_function_local()
on his s390. The problem boils down to:

	CPU-A				CPU-B

	perf_event_overflow()
	  perf_event_disable_inatomic()
	    @pending_disable = 1
	    irq_work_queue();

	sched-out
	  event_sched_out()
	    @pending_disable = 0

					sched-in
					perf_event_overflow()
					  perf_event_disable_inatomic()
					    @pending_disable = 1;
					    irq_work_queue(); // FAILS

	irq_work_run()
	  perf_pending_event()
	    if (@pending_disable)
	      perf_event_disable_local(); // WHOOPS

The problem exists in generic, but s390 is particularly sensitive
because it doesn't implement arch_irq_work_raise(), nor does it call
irq_work_run() from it's PMU interrupt handler (nor would that be
sufficient in this case, because s390 also generates
perf_event_overflow() from pmu::stop). Add to that the fact that s390
is a virtual architecture and (virtual) CPU-A can stall long enough
for the above race to happen, even if it would self-IPI.

Adding a irq_work_sync() to event_sched_in() would work for all hardare
PMUs that properly use irq_work_run() but fails for software PMUs.

Instead encode the CPU number in @pending_disable, such that we can
tell which CPU requested the disable. This then allows us to detect
the above scenario and even redirect the IPI to make up for the failed
queue.

Reported-by: Thomas-Mich Richter 
Tested-by: Thomas Richter 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Mark Rutland 
Cc: Alexander Shishkin 
Cc: Arnaldo Carvalho de Melo 
Cc: Heiko Carstens 
Cc: Hendrik Brueckner 
Cc: Jiri Olsa 
Cc: Kees Cook 
Cc: Linus Torvalds 
Cc: Martin Schwidefsky 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Signed-off-by: Ingo Molnar