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| author | Jann Horn <jannh@google.com> | 2022-03-14 21:59:53 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-04-08 15:23:01 +0300 |
| commit | bc5f440e1c5c86a09b4045049552fd31b5aea293 (patch) | |
| tree | a8d311a1d80f9e5157795f8cd5762ee18e5f62b9 /drivers/firmware | |
| parent | 10a15d91bcbae44ff816ae9a715bfca932734317 (diff) | |
| download | linux-bc5f440e1c5c86a09b4045049552fd31b5aea293.tar.xz | |
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 ea84b580b955 ("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 959217c84c27 ("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: ea84b580b955 ("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>
Diffstat (limited to 'drivers/firmware')
| -rw-r--r-- | drivers/firmware/efi/efi-pstore.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c index 0ef086e43090..7e771c56c13c 100644 --- a/drivers/firmware/efi/efi-pstore.c +++ b/drivers/firmware/efi/efi-pstore.c @@ -266,7 +266,7 @@ static int efi_pstore_write(struct pstore_record *record) efi_name[i] = name[i]; ret = efivar_entry_set_safe(efi_name, vendor, PSTORE_EFI_ATTRIBUTES, - preemptible(), record->size, record->psi->buf); + false, record->size, record->psi->buf); if (record->reason == KMSG_DUMP_OOPS && try_module_get(THIS_MODULE)) if (!schedule_work(&efivar_work)) |