diff options
author | Tony Breeds <tony@bakeyournoodle.com> | 2010-05-19 15:46:36 +1000 |
---|---|---|
committer | Ingo Molnar <mingo@elte.hu> | 2010-05-19 08:18:44 +0200 |
commit | fd6be105b883244127a734ac9f14ae94a022dcc0 (patch) | |
tree | 9fc86c2827813379274522bdc92dd71538d207e5 /lib/proportions.c | |
parent | 537b60d17894b7c19a6060feae40299d7109d6e7 (diff) | |
download | linux-fd6be105b883244127a734ac9f14ae94a022dcc0.tar.bz2 |
mutex: Fix optimistic spinning vs. BKL
Currently, we can hit a nasty case with optimistic
spinning on mutexes:
CPU A tries to take a mutex, while holding the BKL
CPU B tried to take the BLK while holding the mutex
This looks like a AB-BA scenario but in practice, is
allowed and happens due to the auto-release on
schedule() nature of the BKL.
In that case, the optimistic spinning code can get us
into a situation where instead of going to sleep, A
will spin waiting for B who is spinning waiting for
A, and the only way out of that loop is the
need_resched() test in mutex_spin_on_owner().
This patch fixes it by completely disabling spinning
if we own the BKL. This adds one more detail to the
extensive list of reasons why it's a bad idea for
kernel code to be holding the BKL.
Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: <stable@kernel.org>
LKML-Reference: <20100519054636.GC12389@ozlabs.org>
[ added an unlikely() attribute to the branch ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'lib/proportions.c')
0 files changed, 0 insertions, 0 deletions