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author | Linus Torvalds <torvalds@linux-foundation.org> | 2008-04-15 13:09:54 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-04-15 13:09:54 -0700 |
commit | 093a07e2fdfaddab7fc7d4adc76cc569c86603d7 (patch) | |
tree | baaa4d86680347a0687ebfbe133d7b253b88102c /kernel/printk.c | |
parent | 0de19a456cb59106420864927fdec152310f70b6 (diff) | |
download | kernel_samsung_smdk4412-093a07e2fdfaddab7fc7d4adc76cc569c86603d7.zip kernel_samsung_smdk4412-093a07e2fdfaddab7fc7d4adc76cc569c86603d7.tar.gz kernel_samsung_smdk4412-093a07e2fdfaddab7fc7d4adc76cc569c86603d7.tar.bz2 |
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.c | 17 |
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; |