Commit-ID: 0b5e1c5255e7ee8670e077e8224e5c2281229a5b
Gitweb: http://git.kernel.org/tip/0b5e1c5255e7ee8670e077e8224e5c2281229a5b
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Tue, 7 Jun 2011 11:15:33 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 7 Jun 2011 12:50:02 +0200
printk: Release console_sem after logbuf_lock
Release console_sem after unlocking the logbuf_lock so that we don't
generate wakeups while holding logbuf_lock. This avoids some lock
inversion troubles once we remove the lockdep_off bits between
logbuf_lock and rq->lock (prints while holding rq->lock vs doing
wakeups while holding logbuf_lock).
There's of course still an actual deadlock where the printk()s under
rq->lock will issue a wakeup from the up() call, but lockdep won't
warn about that since semaphores are not tracked.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-j8swthl12u73h4znbvitljzd@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
kernel/printk.c | 8 +++++---
1 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/kernel/printk.c b/kernel/printk.c
index 3518539..751e7b8 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -782,7 +782,7 @@ static inline int can_use_console(unsigned int cpu)
static int console_trylock_for_printk(unsigned int cpu)
__releases(&logbuf_lock)
{
- int retval = 0;
+ int retval = 0, wake = 0;
if (console_trylock()) {
retval = 1;
@@ -795,12 +795,14 @@ static int console_trylock_for_printk(unsigned int cpu)
*/
if (!can_use_console(cpu)) {
console_locked = 0;
- up(&console_sem);
+ wake = 1;
retval = 0;
}
}
printk_cpu = UINT_MAX;
spin_unlock(&logbuf_lock);
+ if (wake)
+ up(&console_sem);
return retval;
}
static const char recursion_bug_msg [] =
@@ -1271,8 +1273,8 @@ void console_unlock(void)
if (unlikely(exclusive_console))
exclusive_console = NULL;
- up(&console_sem);
spin_unlock_irqrestore(&logbuf_lock, flags);
+ up(&console_sem);
if (wake_klogd)
wake_up_klogd();
}
--
To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
|