If we don't call mutex_acquire at the beginning of console_unblank, we can run
into a lockup on the logbuf_lock between console_unlock and printk during panic.
What happens in console_unlock is:
-locks logbuf_lock
-calls mutex_release
-which calls printk
-which locks logbuf_lock
This fixes the problem by calling console_trylock (which calls mutex_acquire)
instead of directly accessing the semaphore in console_unblank and moves the
mutex_release to after we unlock logbuf_lock in console_unlock (interrupts are
still disabled).
Signed-off-by: Derek Basehore <dbaseh...@chromium.org>
---
kernel/printk/printk.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 7228258..c599ab5 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2084,7 +2084,6 @@ skip:
local_irq_restore(flags);
}
console_locked = 0;
- mutex_release(&console_lock_dep_map, 1, _RET_IP_);
/* Release the exclusive_console once it is used */
if (unlikely(exclusive_console))
@@ -2092,6 +2091,7 @@ skip:
raw_spin_unlock(&logbuf_lock);
+ mutex_release(&console_lock_dep_map, 1, _RET_IP_);
up(&console_sem);
/*
@@ -2137,7 +2137,7 @@ void console_unblank(void)
* oops_in_progress is set to 1..
*/
if (oops_in_progress) {
- if (down_trylock(&console_sem) != 0)
+ if (!console_trylock())
return;
} else
console_lock();
--
1.9.1.423.g4596e3a
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