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Peter Zijlstra 67009b0cac locking/rtmutex: Fix task->pi_waiters integrity 
[ Upstream commit f7853c3424 ]

Henry reported that rt_mutex_adjust_prio_check() has an ordering
problem and puts the lie to the comment in [7]. Sharing the sort key
between lock->waiters and owner->pi_waiters *does* create problems,
since unlike what the comment claims, holding [L] is insufficient.

Notably, consider:

	A
      /   \
     M1   M2
     |     |
     B     C

That is, task A owns both M1 and M2, B and C block on them. In this
case a concurrent chain walk (B & C) will modify their resp. sort keys
in [7] while holding M1->wait_lock and M2->wait_lock. So holding [L]
is meaningless, they're different Ls.

This then gives rise to a race condition between [7] and [11], where
the requeue of pi_waiters will observe an inconsistent tree order.

	B				C

  (holds M1->wait_lock,		(holds M2->wait_lock,
   holds B->pi_lock)		 holds A->pi_lock)

  [7]
  waiter_update_prio();
  ...
  [8]
  raw_spin_unlock(B->pi_lock);
  ...
  [10]
  raw_spin_lock(A->pi_lock);

				[11]
				rt_mutex_enqueue_pi();
				// observes inconsistent A->pi_waiters
				// tree order

Fixing this means either extending the range of the owner lock from
[10-13] to [6-13], with the immediate problem that this means [6-8]
hold both blocked and owner locks, or duplicating the sort key.

Since the locking in chain walk is horrible enough without having to
consider pi_lock nesting rules, duplicate the sort key instead.

By giving each tree their own sort key, the above race becomes
harmless, if C sees B at the old location, then B will correct things
(if they need correcting) when it walks up the chain and reaches A.

Fixes: fb00aca474 ("rtmutex: Turn the plist into an rb-tree")
Reported-by: Henry Wu <triangletrap12@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Henry Wu <triangletrap12@gmail.com>
Link: https://lkml.kernel.org/r/20230707161052.GF2883469%40hirez.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@kernel.org>
2023-08-20 16:01:25 +08:00
arch KVM: VMX: Don't fudge CR0 and CR4 for restricted L2 guest 2023-08-20 16:01:23 +08:00
block block/partition: fix signedness issue for Amiga partitions 2023-08-20 15:24:51 +08:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2023-04-19 17:50:34 +08:00
crypto KEYS: asymmetric: Copy sig and digest in public_key_verify_signature() 2023-08-20 15:21:12 +08:00
Documentation Documentation: security-bugs.rst: clarify CVE handling 2023-08-20 16:01:24 +08:00
drivers irqchip/gic-v4.1: Properly lock VPEs when doing a directLPI invalidation 2023-08-20 16:01:25 +08:00
fs nfsd: Remove incorrect check in nfsd4_validate_stateid 2023-08-20 16:01:25 +08:00
include block: Fix a source code comment in include/uapi/linux/blkzoned.h 2023-08-20 16:01:22 +08:00
init kbuild: Add CONFIG_PAHOLE_VERSION 2023-04-19 17:59:33 +08:00
io_uring io_uring: don't audit the capability check in io_uring_create() 2023-08-20 16:01:14 +08:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2023-04-19 17:56:54 +08:00
kernel locking/rtmutex: Fix task->pi_waiters integrity 2023-08-20 16:01:25 +08:00
lib test_firmware: return ENOMEM instead of ENOSPC on failed memory allocation 2023-08-20 15:24:43 +08:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/damon/ops-common: atomically test and clear young on ptes and pmds 2023-08-20 15:24:58 +08:00
net tipc: stop tipc crypto on failure in tipc_node_create 2023-08-20 16:01:21 +08:00
samples samples: ftrace: Save required argument registers in sample trampolines 2023-08-20 16:01:05 +08:00
scripts kbuild: Disable GCOV for *.mod.o 2023-08-20 15:24:38 +08:00
security security: keys: Modify mismatched function name 2023-08-20 16:01:12 +08:00
sound ALSA: hda/relatek: Enable Mute LED on HP 250 G8 2023-08-20 16:01:25 +08:00
tools perf build: Fix library not found error when using CSLIBS 2023-08-20 16:01:11 +08:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2023-04-19 17:44:58 +08:00
virt KVM: Grab a reference to KVM for VM and vCPU stats file descriptors 2023-08-20 16:01:23 +08:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS cifs: missing directory in MAINTAINERS file 2023-08-20 16:01:16 +08:00
Makefile Linux 5.15.123 2023-08-20 16:01:14 +08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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.