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Fix locking bug in "acquire_console_semaphore_for_printk()"

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When I cleaned up printk() and split up the printk locking logic in
commit 266c2e0abe ("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>
This commit is contained in:
Linus Torvalds 2008-04-15 13:09:54 -07:00
parent 0de19a456c
commit 093a07e2fd
1 changed files with 15 additions and 2 deletions
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17
kernel/printk.c
View file

@ -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;