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author | Christian Ruppert <christian.ruppert@abilis.com> | 2013-04-08 11:35:30 +0400 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-04-09 03:10:26 +0400 |
commit | 79e5f05edcbf85825d19eb8a425cd6c36c6c66f1 (patch) | |
tree | 974c779a234e6a993fc7d98d93307130fa801221 /arch | |
parent | f465d40d85fa49dd247035c87f519c7c949fbe1d (diff) | |
download | linux-79e5f05edcbf85825d19eb8a425cd6c36c6c66f1.tar.xz |
ARC: Add implicit compiler barrier to raw_local_irq* functions
ARC irqsave/restore macros were missing the compiler barrier, causing a
stale load in irq-enabled region be used in irq-safe region, despite
being changed, because the register holding the value was still live.
The problem manifested as random crashes in timer code when stress
testing ARCLinux (3.9-rc3) on a !SMP && !PREEMPT_COUNT
Here's the exact sequence which caused this:
(0). tv1[x] <----> t1 <---> t2
(1). mod_timer(t1) interrupted after it calls timer_pending()
(2). mod_timer(t2) completes
(3). mod_timer(t1) resumes but messes up the list
(4). __runt_timers( ) uses bogus timer_list entry / crashes in
timer->function
Essentially mod_timer() was racing against itself and while the spinlock
serialized the tv1[] timer link list, timer_pending() called outside the
spinlock, cached timer link list element in a register.
With low register pressure (and a deep register file), lack of barrier
in raw_local_irqsave() as well as preempt_disable (!PREEMPT_COUNT
version), there was nothing to force gcc to reload across the spinlock,
causing a stale value in reg be used for link list manipulation - ensuing
a corruption.
ARcompact disassembly which shows the culprit generated code:
mod_timer:
push_s blink
mov_s r13,r0 # timer, timer
..
###### timer_pending( )
ld_s r3,[r13] # <------ <variable>.entry.next LOADED
brne r3, 0, @.L163
.L163:
..
###### spin_lock_irq( )
lr r5, [status32] # flags
bic r4, r5, 6 # temp, flags,
and.f 0, r5, 6 # flags,
flag.nz r4
###### detach_if_pending( ) begins
tst_s r3,r3 <--------------
# timer_pending( ) checks timer->entry.next
# r3 is NOT reloaded by gcc, using stale value
beq.d @.L169
mov.eq r0,0
##### detach_timer( ): __list_del( )
ld r4,[r13,4] # <variable>.entry.prev, D.31439
st r4,[r3,4] # <variable>.prev, D.31439
st r3,[r4] # <variable>.next, D.30246
We initially tried to fix this by adding barrier() to preempt_* macros
for !PREEMPT_COUNT but Linus clarified that it was anything but wrong.
http://www.spinics.net/lists/kernel/msg1512709.html
[vgupta: updated commitlog]
Reported-by/Signed-off-by: Christian Ruppert <christian.ruppert@abilis.com>
Cc: Christian Ruppert <christian.ruppert@abilis.com>
Cc: Pierrick Hascoet <pierrick.hascoet@abilis.com>
Debugged-by/Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch')
-rw-r--r-- | arch/arc/include/asm/irqflags.h | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/arch/arc/include/asm/irqflags.h b/arch/arc/include/asm/irqflags.h index ccd84806b62f..eac071668201 100644 --- a/arch/arc/include/asm/irqflags.h +++ b/arch/arc/include/asm/irqflags.h @@ -39,7 +39,7 @@ static inline long arch_local_irq_save(void) " flag.nz %0 \n" : "=r"(temp), "=r"(flags) : "n"((STATUS_E1_MASK | STATUS_E2_MASK)) - : "cc"); + : "memory", "cc"); return flags; } @@ -53,7 +53,8 @@ static inline void arch_local_irq_restore(unsigned long flags) __asm__ __volatile__( " flag %0 \n" : - : "r"(flags)); + : "r"(flags) + : "memory"); } /* @@ -73,7 +74,8 @@ static inline void arch_local_irq_disable(void) " and %0, %0, %1 \n" " flag %0 \n" : "=&r"(temp) - : "n"(~(STATUS_E1_MASK | STATUS_E2_MASK))); + : "n"(~(STATUS_E1_MASK | STATUS_E2_MASK)) + : "memory"); } /* @@ -85,7 +87,9 @@ static inline long arch_local_save_flags(void) __asm__ __volatile__( " lr %0, [status32] \n" - : "=&r"(temp)); + : "=&r"(temp) + : + : "memory"); return temp; } |