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Peter Zijlstra f836f9ac95 perf/core: Fix data race between perf_event_set_output() and perf_mmap_close() 
[ Upstream commit 68e3c69803 ]

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: 9bb5d40cd9 ("perf: Fix mmap() accounting hole")
Reported-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Yang Jihong <yangjihong1@huawei.com>
Link: https://lkml.kernel.org/r/YsQ3jm2GR38SW7uD@worktop.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-07-29 17:06:49 +02:00
arch x86: Clear .brk area at early boot 2022-07-21 20:42:47 +02:00
block
certs
crypto
Documentation ipv4: Fix data-races around sysctl_ip_dynaddr. 2022-07-21 20:42:45 +02:00
drivers power/reset: arm-versatile: Fix refcount leak in versatile_reboot_probe 2022-07-29 17:06:49 +02:00
firmware
fs nilfs2: fix incorrect masking of permission flags for symlinks 2022-07-21 20:42:43 +02:00
include net: Fix data-races around sysctl_mem. 2022-07-21 20:42:44 +02:00
init
ipc
kernel perf/core: Fix data race between perf_event_set_output() and perf_mmap_close() 2022-07-29 17:06:49 +02:00
lib ida: don't use BUG_ON() for debugging 2022-07-12 16:27:29 +02:00
mm mm: invalidate hwpoison page cache page in fault path 2022-07-21 20:42:48 +02:00
net xfrm: xfrm_policy: fix a possible double xfrm_pols_put() in xfrm_bundle_lookup() 2022-07-29 17:06:49 +02:00
samples
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sound ASoC: wm5110: Fix DRE control 2022-07-21 20:42:47 +02:00
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Makefile Linux 4.14.289 2022-07-21 20:42:48 +02:00
README

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.