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authorLinus Torvalds <torvalds@linux-foundation.org>2008-04-15 16:09:54 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-15 16:09:54 -0400
commit093a07e2fdfaddab7fc7d4adc76cc569c86603d7 (patch)
treebaaa4d86680347a0687ebfbe133d7b253b88102c /kernel/printk.c
parent0de19a456cb59106420864927fdec152310f70b6 (diff)
Fix locking bug in "acquire_console_semaphore_for_printk()"
When I cleaned up printk() and split up the printk locking logic in commit 266c2e0abeca649fa6667a1a427ad1da507c6375 ("Make printk() console semaphore accesses sensible") I had incorrectly moved the call to have_callable_console() outside of the console semaphore. That was buggy. The console semaphore protects the console_drivers list that is used by have_callable_console(). Thanks go to Bongani Hlope who saw this as a hang on shutdown and reboot and bisected the bug to the right commit, and tested this patch. See http://lkml.org/lkml/2008/4/11/315 Bisected-and-tested-by: Bongani Hlope <bonganilinux@mweb.co.za> Cc: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/printk.c')
-rw-r--r--kernel/printk.c17
1 files changed, 15 insertions, 2 deletions
diff --git a/kernel/printk.c b/kernel/printk.c
index c46a20a19a15..bdd4ea8c3f2b 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -643,8 +643,21 @@ static int acquire_console_semaphore_for_printk(unsigned int cpu)
643{ 643{
644 int retval = 0; 644 int retval = 0;
645 645
646 if (can_use_console(cpu)) 646 if (!try_acquire_console_sem()) {
647 retval = !try_acquire_console_sem(); 647 retval = 1;
648
649 /*
650 * If we can't use the console, we need to release
651 * the console semaphore by hand to avoid flushing
652 * the buffer. We need to hold the console semaphore
653 * in order to do this test safely.
654 */
655 if (!can_use_console(cpu)) {
656 console_locked = 0;
657 up(&console_sem);
658 retval = 0;
659 }
660 }
648 printk_cpu = UINT_MAX; 661 printk_cpu = UINT_MAX;
649 spin_unlock(&logbuf_lock); 662 spin_unlock(&logbuf_lock);
650 return retval; 663 return retval;