printk: Release console_sem after logbuf_lock
Commit-ID: 0b5e1c5255e7ee8670e077e8224e5c2281229a5b Gitweb: http://git.kernel.org/tip/0b5e1c5255e7ee8670e077e8224e5c2281229a5b Author: Peter Zijlstra <[email protected]> AuthorDate: Tue, 7 Jun 2011 11:15:33 +0200 Committer: Ingo Molnar <[email protected]> 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 <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Andrew Morton <[email protected]>
Signed-off-by Ingo Molnar <[email protected]>
--- kernel/printk.c | 8 +++++--- 1 files changed, 5 insertions(+), 3 deletions(-)
kernel/printk.c +5 -3
@@ -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 (); }