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authorJann Horn <jannh@google.com>2022-03-14 21:59:53 +0300
committerKees Cook <keescook@chromium.org>2022-03-15 21:08:23 +0300
commit8126b1c73108bc691f5643df19071a59a69d0bc6 (patch)
tree1f12c87abbea4a39725bf0b1a9e839682c578e64 /fs/pstore/platform.c
parent023bbde3db41078780f5d57e5354212f974c4bca (diff)
downloadlinux-8126b1c73108bc691f5643df19071a59a69d0bc6.tar.xz
pstore: Don't use semaphores in always-atomic-context code
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
Diffstat (limited to 'fs/pstore/platform.c')
-rw-r--r--fs/pstore/platform.c38
1 files changed, 18 insertions, 20 deletions
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index f243cb5e6a4f..e26162f102ff 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -143,21 +143,22 @@ static void pstore_timer_kick(void)
mod_timer(&pstore_timer, jiffies + msecs_to_jiffies(pstore_update_ms));
}
-/*
- * Should pstore_dump() wait for a concurrent pstore_dump()? If
- * not, the current pstore_dump() will report a failure to dump
- * and return.
- */
-static bool pstore_cannot_wait(enum kmsg_dump_reason reason)
+static bool pstore_cannot_block_path(enum kmsg_dump_reason reason)
{
- /* In NMI path, pstore shouldn't block regardless of reason. */
+ /*
+ * In case of NMI path, pstore shouldn't be blocked
+ * regardless of reason.
+ */
if (in_nmi())
return true;
switch (reason) {
/* In panic case, other cpus are stopped by smp_send_stop(). */
case KMSG_DUMP_PANIC:
- /* Emergency restart shouldn't be blocked. */
+ /*
+ * Emergency restart shouldn't be blocked by spinning on
+ * pstore_info::buf_lock.
+ */
case KMSG_DUMP_EMERG:
return true;
default:
@@ -389,21 +390,19 @@ static void pstore_dump(struct kmsg_dumper *dumper,
unsigned long total = 0;
const char *why;
unsigned int part = 1;
+ unsigned long flags = 0;
int ret;
why = kmsg_dump_reason_str(reason);
- if (down_trylock(&psinfo->buf_lock)) {
- /* Failed to acquire lock: give up if we cannot wait. */
- if (pstore_cannot_wait(reason)) {
- pr_err("dump skipped in %s path: may corrupt error record\n",
- in_nmi() ? "NMI" : why);
- return;
- }
- if (down_interruptible(&psinfo->buf_lock)) {
- pr_err("could not grab semaphore?!\n");
+ if (pstore_cannot_block_path(reason)) {
+ if (!spin_trylock_irqsave(&psinfo->buf_lock, flags)) {
+ pr_err("dump skipped in %s path because of concurrent dump\n",
+ in_nmi() ? "NMI" : why);
return;
}
+ } else {
+ spin_lock_irqsave(&psinfo->buf_lock, flags);
}
kmsg_dump_rewind(&iter);
@@ -467,8 +466,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
total += record.size;
part++;
}
-
- up(&psinfo->buf_lock);
+ spin_unlock_irqrestore(&psinfo->buf_lock, flags);
}
static struct kmsg_dumper pstore_dumper = {
@@ -594,7 +592,7 @@ int pstore_register(struct pstore_info *psi)
psi->write_user = pstore_write_user_compat;
psinfo = psi;
mutex_init(&psinfo->read_mutex);
- sema_init(&psinfo->buf_lock, 1);
+ spin_lock_init(&psinfo->buf_lock);
if (psi->flags & PSTORE_FLAGS_DMESG)
allocate_buf_for_compression();