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authorLinus Torvalds <torvalds@linux-foundation.org>2008-04-15 13:09:54 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-15 13:09:54 -0700
commit093a07e2fdfaddab7fc7d4adc76cc569c86603d7 (patch)
treebaaa4d86680347a0687ebfbe133d7b253b88102c
parent0de19a456cb59106420864927fdec152310f70b6 (diff)
downloadlinux-093a07e2fdfaddab7fc7d4adc76cc569c86603d7.tar.gz
linux-093a07e2fdfaddab7fc7d4adc76cc569c86603d7.tar.xz
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>
-rw-r--r--kernel/printk.c17
1 files changed, 15 insertions, 2 deletions
diff --git a/kernel/printk.c b/kernel/printk.c
index c46a20a..bdd4ea8 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -643,8 +643,21 @@ static int acquire_console_semaphore_for_printk(unsigned int cpu)
{
int retval = 0;
- if (can_use_console(cpu))
- retval = !try_acquire_console_sem();
+ if (!try_acquire_console_sem()) {
+ retval = 1;
+
+ /*
+ * If we can't use the console, we need to release
+ * the console semaphore by hand to avoid flushing
+ * the buffer. We need to hold the console semaphore
+ * in order to do this test safely.
+ */
+ if (!can_use_console(cpu)) {
+ console_locked = 0;
+ up(&console_sem);
+ retval = 0;
+ }
+ }
printk_cpu = UINT_MAX;
spin_unlock(&logbuf_lock);
return retval;