powerpc/powernv: recheck lock bit in core_idle_lock_held after lwarx
RFC PATCH 1/1 powerpc/powernv: recheck lock bit in core_idle_lock_held after lwarx
The core_idle_lock_held loops when the lock bit is held by others. However, it is possible that after the lock bit is cleared, some one else sees it first and sets the lock bit. And lwarx loads a value with lock bit set, and the lock bit may be cleared in the following stwcx. It is possible the first one is still executing in the critical section.
This patch rechecks the lock bit after lwarx, and go back to loop if it is set.
--- arch/powerpc/kernel/idle_book3s.S | 2 ++ 1 file changed, 2 insertions(+)
arch/powerpc/kernel/idle_book3s.S +2 -0
@@ -99,6 +99,8 @@ core_idle_lock_held: bne 3b HMT_MEDIUM lwarx r15,0,r14 + andi. r9,r15,PNV_CORE_IDLE_LOCK_BIT + bne- core_idle_lock_held blr /*
Signature · 1 line
1.9.1
Quoted 8 lines · Li Zhong
The
core_idle_lock_heldloops when the lock bit is held by others. However, it is possible that after the lock bit is cleared, some one else sees it first and sets the lock bit. And lwarx loads a value with lock bit set, and the lock bit may be cleared in the following stwcx. It is possible the first one is still executing in the critical section.This patch rechecks the lock bit after lwarx, and go back to loop if it is set.
You're quite correct, in fact I posted almost exactly the same patch a few days ago... See http://patchwork.ozlabs.org/patch/684963/.
Thanks,
Paul.
Quoted 7 lines · Paul Mackerras
=20
Quoted 3 lines · Li Zhong
The
core_idle_lock_heldloops when the lock bit is held by others. However, it is possible that after the lock bit is cleared, some one else sees it first and sets the lock bit. And lwarx loads a value =
with
Quoted 2 lines
Quoted 2 lines
lock bit set, and the lock bit may be cleared in the following stwcx. It is possible the first one is still executing in the critical =
section.
Quoted 2 lines
Quoted 2 lines
=20
This patch rechecks the lock bit after lwarx, and go back to loop if =
it
Quoted 4 lines
Quoted 1 line
is set.
=20
You're quite correct, in fact I posted almost exactly the same patch a few days ago... See http://patchwork.ozlabs.org/patch/684963/.
Forget to check the list before sending =E2=80=A6=20
One minor difference, maybe we can use bne- for the rechecking :)
Thanks, Zhong
Quoted 4 lines
=20
Thanks,
Paul.
=20