Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash
From: Eugeniy.Paltsev@synopsys.com (Eugeniy Paltsev)
Date: 2018-08-30 14:47:10
Also in:
linux-arch, lkml
On Thu, 2018-08-30 at 16:17 +0200, Peter Zijlstra wrote:
On Thu, Aug 30, 2018 at 11:53:17AM +0000, Eugeniy Paltsev wrote:quoted
I can see crashes with LLSC enabled in both SMP running on 4 cores and SMP running on 1 core.So you're running on LL/SC enabled hardware; that would make Will's patch irrelevant (although still a good idea for the hardware that does care about that spinlocked atomic crud). Does something like the below cure things? That would confirm the suggestion that the change to __clear_bit_unlock() is the curprit.
I tested it - this doesn't change anything, the problem still reproduces. I'll test it with last Will fix.
quoted hunk ↗ jump to hunk
If that doesn't cure things, then we've been looking in entirely the wrong place. ---diff --git a/include/asm-generic/bitops/lock.h b/include/asm-generic/bitops/lock.h index 3ae021368f48..79c6978152f8 100644 --- a/include/asm-generic/bitops/lock.h +++ b/include/asm-generic/bitops/lock.h@@ -57,12 +57,7 @@ static inline void clear_bit_unlock(unsigned int nr, volatile unsigned long *p) static inline void __clear_bit_unlock(unsigned int nr, volatile unsigned long *p) { - unsigned long old; - - p += BIT_WORD(nr); - old = READ_ONCE(*p); - old &= ~BIT_MASK(nr); - atomic_long_set_release((atomic_long_t *)p, old); + clear_bit_unlock(nr, p); } /**
-- Eugeniy Paltsev