Messages in this thread | | | From | Qian Cai <> | Date | Tue, 19 May 2020 17:10:36 -0400 | Subject | Re: [PATCH] READ_ONCE, WRITE_ONCE, kcsan: Perform checks in __*_ONCE variants |
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On Tue, May 12, 2020 at 3:09 PM Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, May 12, 2020 at 08:38:39PM +0200, Marco Elver wrote: > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > > index 741c93c62ecf..e902ca5de811 100644 > > --- a/include/linux/compiler.h > > +++ b/include/linux/compiler.h > > @@ -224,13 +224,16 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, > > * atomicity or dependency ordering guarantees. Note that this may result > > * in tears! > > */ > > -#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x)) > > +#define __READ_ONCE(x) \ > > +({ \ > > + kcsan_check_atomic_read(&(x), sizeof(x)); \ > > + data_race((*(const volatile __unqual_scalar_typeof(x) *)&(x))); \ > > +}) > > NAK > > This will actively insert instrumentation into __READ_ONCE() and I need > it to not have any.
Any way to move this forward? Due to linux-next commit 6bcc8f459fe7 (locking/atomics: Flip fallbacks and instrumentation), it triggers a lots of KCSAN warnings due to atomic ops are no longer marked. For example,
[ 197.318288][ T1041] write to 0xffff9302764ccc78 of 8 bytes by task 1048 on cpu 47: [ 197.353119][ T1041] down_read_trylock+0x9e/0x1e0 atomic_long_set(&sem->owner, val); __rwsem_set_reader_owned at kernel/locking/rwsem.c:205 (inlined by) rwsem_set_reader_owned at kernel/locking/rwsem.c:213 (inlined by) __down_read_trylock at kernel/locking/rwsem.c:1373 (inlined by) down_read_trylock at kernel/locking/rwsem.c:1517 [ 197.374641][ T1041] page_lock_anon_vma_read+0x19d/0x3c0 [ 197.398894][ T1041] rmap_walk_anon+0x30e/0x620
[ 197.924695][ T1041] read to 0xffff9302764ccc78 of 8 bytes by task 1041 on cpu 43: [ 197.959501][ T1041] up_read+0xb8/0x41a arch_atomic64_read at arch/x86/include/asm/atomic64_64.h:22 (inlined by) atomic64_read at include/asm-generic/atomic-instrumented.h:838 (inlined by) atomic_long_read at include/asm-generic/atomic-long.h:29 (inlined by) rwsem_clear_reader_owned at kernel/locking/rwsem.c:242 (inlined by) __up_read at kernel/locking/rwsem.c:1433 (inlined by) up_read at kernel/locking/rwsem.c:1574 [ 197.977728][ T1041] rmap_walk_anon+0x2f2/0x620 [ 197.999055][ T1041] rmap_walk+0xb5/0xe0
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