Jann Horn 86a926c3f0 pstore: Don't use semaphores in always-atomic-context code ... commit 8126b1c73108bc691f5643df19071a59a69d0bc6 upstream. pstore_dump() is *always* invoked in atomic context (nowadays in an RCU read-side critical section, before that under a spinlock). It doesn't make sense to try to use semaphores here. This is mostly a revert of commit ea84b580b9 ("pstore: Convert buf_lock to semaphore"), except that two parts aren't restored back exactly as they were: - keep the lock initialization in pstore_register - in efi_pstore_write(), always set the "block" flag to false - omit "is_locked", that was unnecessary since commit 959217c84c ("pstore: Actually give up during locking failure") - fix the bailout message The actual problem that the buggy commit was trying to address may have been that the use of preemptible() in efi_pstore_write() was wrong - it only looks at preempt_count() and the state of IRQs, but __rcu_read_lock() doesn't touch either of those under CONFIG_PREEMPT_RCU. (Sidenote: CONFIG_PREEMPT_RCU means that the scheduler can preempt tasks in RCU read-side critical sections, but you're not allowed to actively block/reschedule.) Lockdep probably never caught the problem because it's very rare that you actually hit the contended case, so lockdep always just sees the down_trylock(), not the down_interruptible(), and so it can't tell that there's a problem. Fixes: ea84b580b9 ("pstore: Convert buf_lock to semaphore") Cc: stable@vger.kernel.org Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20220314185953.2068993-1-jannh@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2022-04-08 14:39:56 +02:00
..
Kconfig	mark pstore-blk as broken	2021-07-14 16:56:12 +02:00
Makefile	pstore/blk: Introduce backend for block devices	2020-05-30 10:34:03 -07:00
blk.c	pstore/blk: Introduce "best_effort" mode	2020-05-31 19:49:01 -07:00
ftrace.c	pstore/ftrace: Provide ftrace log merging routine	2020-05-30 10:34:02 -07:00
inode.c	pstore: Fix warning in pstore_kill_sb()	2021-03-25 09:04:08 +01:00
internal.h	pstore/ftrace: Provide ftrace log merging routine	2020-05-30 10:34:02 -07:00
platform.c	pstore: Don't use semaphores in always-atomic-context code	2022-04-08 14:39:56 +02:00
pmsg.c	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 282	2019-06-05 17:36:37 +02:00
ram.c	pstore/ram: Introduce max_reason and convert dump_oops	2020-05-30 10:34:03 -07:00
ram_core.c	pstore: switch to copy_from_user()	2020-04-23 10:52:48 -04:00
zone.c	treewide: Use fallthrough pseudo-keyword	2020-08-23 17:36:59 -05:00