Nicolas Pitre wrote:
Currently a simple
void foo(void) { preempt_enable(); }
produces the following code on ARM:
foo:
bic r3, sp, #8128
bic r3, r3, #63
ldr r2, [r3, #4]
ldr r1, [r3, #0]
sub r2, r2, #1
tst r1, #4
str r2, [r3, #4]
blne preempt_schedule
mov pc, lr
The problem is that the TIF_NEED_RESCHED flag is loaded _before_ the
preemption count is stored back, hence any interrupt coming within that
3 instruction window causing TIF_NEED_RESCHED to be set won't be
seen and scheduling won't happen as it should.
Nothing currently prevents gcc from performing that reordering. There
is already a barrier() before the decrement of the preemption count, but
another one is needed between this and the TIF_NEED_RESCHED flag test
for proper code ordering.
Nice catch, this is not ARM specific either of course.
kernel/sched.c:preempt_schedule() has an equivalent barrier after
subtracting the preempt count and before checking TIF_NEED_RESCHED,
so I think this is the correct fix.
Linus will you apply?
Signed-off-by: Nicolas Pitre <[email protected]>
---
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index d9a2f52..5769d14 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -48,6 +48,7 @@ do { \
#define preempt_enable() \
do { \
preempt_enable_no_resched(); \
+ barrier(); \
preempt_check_resched(); \
} while (0)
--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]