linux.git/kernel/events, branch v5.15.71

perf/core: Fix data race between perf_event_set_output() and perf_mmap_close()

2022-07-29T15:25:11+00:00

[ Upstream commit 68e3c69803dada336893640110cb87221bb01dcf ]

Yang Jihing reported a race between perf_event_set_output() and
perf_mmap_close():

	CPU1					CPU2

	perf_mmap_close(e2)
	  if (atomic_dec_and_test(&e2->rb->mmap_count)) // 1 - > 0
	    detach_rest = true

						ioctl(e1, IOC_SET_OUTPUT, e2)
						  perf_event_set_output(e1, e2)

	  ...
	  list_for_each_entry_rcu(e, &e2->rb->event_list, rb_entry)
	    ring_buffer_attach(e, NULL);
	    // e1 isn't yet added and
	    // therefore not detached

						    ring_buffer_attach(e1, e2->rb)
						      list_add_rcu(&e1->rb_entry,
								   &e2->rb->event_list)

After this; e1 is attached to an unmapped rb and a subsequent
perf_mmap() will loop forever more:

	again:
		mutex_lock(&e->mmap_mutex);
		if (event->rb) {
			...
			if (!atomic_inc_not_zero(&e->rb->mmap_count)) {
				...
				mutex_unlock(&e->mmap_mutex);
				goto again;
			}
		}

The loop in perf_mmap_close() holds e2->mmap_mutex, while the attach
in perf_event_set_output() holds e1->mmap_mutex. As such there is no
serialization to avoid this race.

Change perf_event_set_output() to take both e1->mmap_mutex and
e2->mmap_mutex to alleviate that problem. Additionally, have the loop
in perf_mmap() detach the rb directly, this avoids having to wait for
the concurrent perf_mmap_close() to get around to doing it to make
progress.

Fixes: 9bb5d40cd93c ("perf: Fix mmap() accounting hole")
Reported-by: Yang Jihong 
Signed-off-by: Peter Zijlstra (Intel) 
Tested-by: Yang Jihong 
Link: https://lkml.kernel.org/r/YsQ3jm2GR38SW7uD@worktop.programming.kicks-ass.net
Signed-off-by: Sasha Levin

signal: Deliver SIGTRAP on perf event asynchronously if blocked

2022-06-09T08:22:48+00:00

[ Upstream commit 78ed93d72ded679e3caf0758357209887bda885f ]

With SIGTRAP on perf events, we have encountered termination of
processes due to user space attempting to block delivery of SIGTRAP.
Consider this case:

    
    ...
    sigset_t s;
    sigemptyset(&s);
    sigaddset(&s, SIGTRAP | );
    sigprocmask(SIG_BLOCK, &s, ...);
    ...
    

When the perf event triggers, while SIGTRAP is blocked, force_sig_perf()
will force the signal, but revert back to the default handler, thus
terminating the task.

This makes sense for error conditions, but not so much for explicitly
requested monitoring. However, the expectation is still that signals
generated by perf events are synchronous, which will no longer be the
case if the signal is blocked and delivered later.

To give user space the ability to clearly distinguish synchronous from
asynchronous signals, introduce siginfo_t::si_perf_flags and
TRAP_PERF_FLAG_ASYNC (opted for flags in case more binary information is
required in future).

The resolution to the problem is then to (a) no longer force the signal
(avoiding the terminations), but (b) tell user space via si_perf_flags
if the signal was synchronous or not, so that such signals can be
handled differently (e.g. let user space decide to ignore or consider
the data imprecise).

The alternative of making the kernel ignore SIGTRAP on perf events if
the signal is blocked may work for some usecases, but likely causes
issues in others that then have to revert back to interception of
sigprocmask() (which we want to avoid). [ A concrete example: when using
breakpoint perf events to track data-flow, in a region of code where
signals are blocked, data-flow can no longer be tracked accurately.
When a relevant asynchronous signal is received after unblocking the
signal, the data-flow tracking logic needs to know its state is
imprecise. ]

Fixes: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events")
Reported-by: Dmitry Vyukov 
Signed-off-by: Marco Elver 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Geert Uytterhoeven 
Tested-by: Dmitry Vyukov 
Link: https://lore.kernel.org/r/20220404111204.935357-1-elver@google.com
Signed-off-by: Sasha Levin

perf: Fix sys_perf_event_open() race against self

2022-05-25T07:57:27+00:00

commit 3ac6487e584a1eb54071dbe1212e05b884136704 upstream.

Norbert reported that it's possible to race sys_perf_event_open() such
that the looser ends up in another context from the group leader,
triggering many WARNs.

The move_group case checks for races against itself, but the
!move_group case doesn't, seemingly relying on the previous
group_leader->ctx == ctx check. However, that check is racy due to not
holding any locks at that time.

Therefore, re-check the result after acquiring locks and bailing
if they no longer match.

Additionally, clarify the not_move_group case from the
move_group-vs-move_group race.

Fixes: f63a8daa5812 ("perf: Fix event->ctx locking")
Reported-by: Norbert Slusarek 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

perf/core: Fix perf_mmap fail when CONFIG_PERF_USE_VMALLOC enabled

2022-04-27T12:38:58+00:00

[ Upstream commit 60490e7966659b26d74bf1fa4aa8693d9a94ca88 ]

This problem can be reproduced with CONFIG_PERF_USE_VMALLOC enabled on
both x86_64 and aarch64 arch when using sysdig -B(using ebpf)[1].
sysdig -B works fine after rebuilding the kernel with
CONFIG_PERF_USE_VMALLOC disabled.

I tracked it down to the if condition event->rb->nr_pages != nr_pages
in perf_mmap is true when CONFIG_PERF_USE_VMALLOC is enabled where
event->rb->nr_pages = 1 and nr_pages = 2048 resulting perf_mmap to
return -EINVAL. This is because when CONFIG_PERF_USE_VMALLOC is
enabled, rb->nr_pages is always equal to 1.

Arch with CONFIG_PERF_USE_VMALLOC enabled by default:
	arc/arm/csky/mips/sh/sparc/xtensa

Arch with CONFIG_PERF_USE_VMALLOC disabled by default:
	x86_64/aarch64/...

Fix this problem by using data_page_nr()

[1] https://github.com/draios/sysdig

Fixes: 906010b2134e ("perf_event: Provide vmalloc() based mmap() backing")
Signed-off-by: Zhipeng Xie 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20220209145417.6495-1-xiezhipeng1@huawei.com
Signed-off-by: Sasha Levin

perf/core: Inherit event_caps

2022-04-13T18:59:24+00:00

commit e3265a4386428d3d157d9565bb520aabff8b4bf0 upstream.

It was reported that some perf event setup can make fork failed on
ARM64.  It was the case of a group of mixed hw and sw events and it
failed in perf_event_init_task() due to armpmu_event_init().

The ARM PMU code checks if all the events in a group belong to the
same PMU except for software events.  But it didn't set the event_caps
of inherited events and no longer identify them as software events.
Therefore the test failed in a child process.

A simple reproducer is:

  $ perf stat -e '{cycles,cs,instructions}' perf bench sched messaging
  # Running 'sched/messaging' benchmark:
  perf: fork(): Invalid argument

The perf stat was fine but the perf bench failed in fork().  Let's
inherit the event caps from the parent.

Signed-off-by: Namhyung Kim 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: 
Link: https://lkml.kernel.org/r/20220328200112.457740-1-namhyung@kernel.org
Signed-off-by: Greg Kroah-Hartman

perf/core: Fix address filter parser for multiple filters

2022-04-08T12:23:10+00:00

[ Upstream commit d680ff24e9e14444c63945b43a37ede7cd6958f9 ]

Reset appropriate variables in the parser loop between parsing separate
filters, so that they do not interfere with parsing the next filter.

Fixes: 375637bc524952 ("perf/core: Introduce address range filtering")
Signed-off-by: Adrian Hunter 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20220131072453.2839535-4-adrian.hunter@intel.com
Signed-off-by: Sasha Levin

perf: Fix list corruption in perf_cgroup_switch()

2022-02-16T11:56:41+00:00

commit 5f4e5ce638e6a490b976ade4a40017b40abb2da0 upstream.

There's list corruption on cgrp_cpuctx_list. This happens on the
following path:

  perf_cgroup_switch: list_for_each_entry(cgrp_cpuctx_list)
      cpu_ctx_sched_in
         ctx_sched_in
            ctx_pinned_sched_in
              merge_sched_in
                  perf_cgroup_event_disable: remove the event from the list

Use list_for_each_entry_safe() to allow removing an entry during
iteration.

Fixes: 058fe1c0440e ("perf/core: Make cgroup switch visit only cpuctxs with cgroup events")
Signed-off-by: Song Liu 
Reviewed-by: Rik van Riel 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20220204004057.2961252-1-song@kernel.org
Signed-off-by: Greg Kroah-Hartman

perf: Always wake the parent event

2022-02-16T11:56:15+00:00

[ Upstream commit 961c39121759ad09a89598ec4ccdd34ae0468a19 ]

When using per-process mode and event inheritance is set to true,
forked processes will create a new perf events via inherit_event() ->
perf_event_alloc(). But these events will not have ring buffers
assigned to them. Any call to wakeup will be dropped if it's called on
an event with no ring buffer assigned because that's the object that
holds the wakeup list.

If the child event is disabled due to a call to
perf_aux_output_begin() or perf_aux_output_end(), the wakeup is
dropped leaving userspace hanging forever on the poll.

Normally the event is explicitly re-enabled by userspace after it
wakes up to read the aux data, but in this case it does not get woken
up so the event remains disabled.

This can be reproduced when using Arm SPE and 'stress' which forks once
before running the workload. By looking at the list of aux buffers read,
it's apparent that they stop after the fork:

  perf record -e arm_spe// -vvv -- stress -c 1

With this patch applied they continue to be printed. This behaviour
doesn't happen when using systemwide or per-cpu mode.

Reported-by: Ruben Ayrapetyan 
Signed-off-by: James Clark 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20211206113840.130802-2-james.clark@arm.com
Signed-off-by: Sasha Levin

perf: Copy perf_event_attr::sig_data on modification

2022-02-08T17:34:12+00:00

[ Upstream commit 3c25fc97f5590060464cabfa25710970ecddbc96 ]

The intent has always been that perf_event_attr::sig_data should also be
modifiable along with PERF_EVENT_IOC_MODIFY_ATTRIBUTES, because it is
observable by user space if SIGTRAP on events is requested.

Currently only PERF_TYPE_BREAKPOINT is modifiable, and explicitly copies
relevant breakpoint-related attributes in hw_breakpoint_copy_attr().
This misses copying perf_event_attr::sig_data.

Since sig_data is not specific to PERF_TYPE_BREAKPOINT, introduce a
helper to copy generic event-type-independent attributes on
modification.

Fixes: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events")
Reported-by: Dmitry Vyukov 
Signed-off-by: Marco Elver 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Dmitry Vyukov 
Link: https://lore.kernel.org/r/20220131103407.1971678-1-elver@google.com
Signed-off-by: Sasha Levin

perf/core: Fix cgroup event list management

2022-02-01T16:27:15+00:00

commit c5de60cd622a2607c043ba65e25a6e9998a369f9 upstream.

The active cgroup events are managed in the per-cpu cgrp_cpuctx_list.
This list is only accessed from current cpu and not protected by any
locks.  But from the commit ef54c1a476ae ("perf: Rework
perf_event_exit_event()"), it's possible to access (actually modify)
the list from another cpu.

In the perf_remove_from_context(), it can remove an event from the
context without an IPI when the context is not active.  This is not
safe with cgroup events which can have some active events in the
context even if ctx->is_active is 0 at the moment.  The target cpu
might be in the middle of list iteration at the same time.

If the event is enabled when it's about to be closed, it might call
perf_cgroup_event_disable() and list_del() with the cgrp_cpuctx_list
on a different cpu.

This resulted in a crash due to an invalid list pointer access during
the cgroup list traversal on the cpu which the event belongs to.

Let's fallback to IPI to access the cgrp_cpuctx_list from that cpu.
Similarly, perf_install_in_context() should use IPI for the cgroup
events too.

Fixes: ef54c1a476ae ("perf: Rework perf_event_exit_event()")
Signed-off-by: Namhyung Kim 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20220124195808.2252071-1-namhyung@kernel.org
Signed-off-by: Greg Kroah-Hartman 
Signed-off-by: Sasha Levin