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James Clark 4f64a6c9f6 perf: Fix perf_event_pmu_context serialization
Syzkaller triggered a WARN in put_pmu_ctx().

  WARNING: CPU: 1 PID: 2245 at kernel/events/core.c:4925 put_pmu_ctx+0x1f0/0x278

This is because there is no locking around the access of "if
(!epc->ctx)" in find_get_pmu_context() and when it is set to NULL in
put_pmu_ctx().

The decrement of the reference count in put_pmu_ctx() also happens
outside of the spinlock, leading to the possibility of this order of
events, and the context being cleared in put_pmu_ctx(), after its
refcount is non zero:

 CPU0                                   CPU1
 find_get_pmu_context()
   if (!epc->ctx) == false
                                        put_pmu_ctx()
                                        atomic_dec_and_test(&epc->refcount) == true
                                        epc->refcount == 0
     atomic_inc(&epc->refcount);
     epc->refcount == 1
                                        list_del_init(&epc->pmu_ctx_entry);
	                                      epc->ctx = NULL;

Another issue is that WARN_ON for no active PMU events in put_pmu_ctx()
is outside of the lock. If the perf_event_pmu_context is an embedded
one, even after clearing it, it won't be deleted and can be re-used. So
the warning can trigger. For this reason it also needs to be moved
inside the lock.

The above warning is very quick to trigger on Arm by running these two
commands at the same time:

  while true; do perf record -- ls; done
  while true; do perf record -- ls; done

[peterz: atomic_dec_and_raw_lock*()]
Fixes: bd27568117 ("perf: Rewrite core context handling")
Reported-by: syzbot+697196bc0265049822bd@syzkaller.appspotmail.com
Signed-off-by: James Clark <james.clark@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lore.kernel.org/r/20230127143141.1782804-2-james.clark@arm.com
2023-01-31 20:37:18 +01:00
arch - Start checking for -mindirect-branch-cs-prefix clang support too now that LLVM 2023-01-29 11:17:34 -08:00
block block-6.2-2023-01-20 2023-01-20 12:44:41 -08:00
certs certs: make system keyring depend on built-in x509 parser 2022-09-24 04:31:18 +09:00
crypto This update includes the following changes: 2022-12-14 12:31:09 -08:00
Documentation - Start checking for -mindirect-branch-cs-prefix clang support too now that LLVM 2023-01-29 11:17:34 -08:00
drivers - Start checking for -mindirect-branch-cs-prefix clang support too now that LLVM 2023-01-29 11:17:34 -08:00
fs 4 smb3 server fixes, all also for stable 2023-01-28 10:52:51 -08:00
include perf: Fix perf_event_pmu_context serialization 2023-01-31 20:37:18 +01:00
init Kbuild fixes for v6.2 (3rd) 2023-01-21 10:56:37 -08:00
io_uring io_uring: always prep_async for drain requests 2023-01-27 06:29:29 -07:00
ipc Non-MM patches for 6.2-rc1. 2022-12-12 17:28:58 -08:00
kernel perf: Fix perf_event_pmu_context serialization 2023-01-31 20:37:18 +01:00
lib perf: Fix perf_event_pmu_context serialization 2023-01-31 20:37:18 +01:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm Revert "mm/compaction: fix set skip in fast_find_migrateblock" 2023-01-29 10:38:43 -08:00
net net: mctp: mark socks as dead on unhash, prevent re-add 2023-01-25 13:07:37 +00:00
rust rust: print: avoid evaluating arguments in pr_* macros in unsafe blocks 2023-01-16 00:54:35 +01:00
samples ftrace: Export ftrace_free_filter() to modules 2023-01-24 11:20:58 -05:00
scripts Fix up more non-executable files marked executable 2023-01-28 11:17:57 -08:00
security tomoyo: Update website link 2023-01-13 23:11:38 +09:00
sound treewide: fix up files incorrectly marked executable 2023-01-26 10:05:39 -08:00
tools gpio fixes for v6.2-rc6 2023-01-27 13:47:40 -08:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt VFIO fixes for v6.2-rc6 2023-01-23 11:56:07 -08:00
.clang-format iommufd for 6.2 2022-12-14 09:15:43 -08:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore *.rpm 2022-12-30 17:22:14 +09:00
.mailmap 21 hotfixes. Thirteen of these address pre-6.1 issues and hence have 2023-01-16 16:36:39 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Update MPTCP maintainer list and CREDITS 2023-01-23 21:42:13 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Tracing updates for 6.2: 2023-01-27 16:03:32 -08:00
Makefile Linux 6.2-rc6 2023-01-29 13:59:43 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

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.