Messages in this thread | | | Subject | Re: [PATCH -next v2] locking/osq_lock: annotate a data race in osq_lock | From | Qian Cai <> | Date | Fri, 8 May 2020 16:59:05 -0400 |
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> On Feb 11, 2020, at 8:54 AM, Qian Cai <cai@lca.pw> wrote: > > prev->next could be accessed concurrently as noticed by KCSAN, > > write (marked) to 0xffff9d3370dbbe40 of 8 bytes by task 3294 on cpu 107: > osq_lock+0x25f/0x350 > osq_wait_next at kernel/locking/osq_lock.c:79 > (inlined by) osq_lock at kernel/locking/osq_lock.c:185 > rwsem_optimistic_spin > <snip> > > read to 0xffff9d3370dbbe40 of 8 bytes by task 3398 on cpu 100: > osq_lock+0x196/0x350 > osq_lock at kernel/locking/osq_lock.c:157 > rwsem_optimistic_spin > <snip> > > Since the write only stores NULL to prev->next and the read tests if > prev->next equals to this_cpu_ptr(&osq_node). Even if the value is > shattered, the code is still working correctly. Thus, mark it as an > intentional data race using the data_race() macro. > > Signed-off-by: Qian Cai <cai@lca.pw>
Hmm, this patch has been dropped from linux-next from some reasons.
Paul, can you pick this up along with KCSAN fixes?
https://lore.kernel.org/lkml/1581429255-12542-1-git-send-email-cai@lca.pw/
> --- > > v2: insert some code comments. > > kernel/locking/osq_lock.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c > index 1f7734949ac8..f733bcd99e8a 100644 > --- a/kernel/locking/osq_lock.c > +++ b/kernel/locking/osq_lock.c > @@ -154,7 +154,11 @@ bool osq_lock(struct optimistic_spin_queue *lock) > */ > > for (;;) { > - if (prev->next == node && > + /* > + * cpu_relax() below implies a compiler barrier which would > + * prevent this comparison being optimized away. > + */ > + if (data_race(prev->next == node) && > cmpxchg(&prev->next, node, NULL) == node) > break; > > -- > 1.8.3.1 >
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