Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
> On Mon, Oct 17, 2016 at 03:40:24PM -0400, Jeff Moyer wrote:
>> Christoph Hellwig <hch@xxxxxx> writes:
>>
>> > On Mon, Oct 17, 2016 at 02:19:47PM -0400, Jeff Moyer wrote:
>> >> This ends up being a call to __sb_end_write:
>> >>
>> >> void __sb_end_write(struct super_block *sb, int level)
>> >> {
>> >> percpu_up_read(sb->s_writers.rw_sem + level-1);
>> >> }
>> >>
>> >> Nothing guarantees that submission and completion happen on the same
>> >> CPU. Is this safe?
>> >
>> > Good point. From my reading of the percpu_rwsem implementation it
>> > is not safe to release it from a different CPU. Which makes me
>> > wonder how we can protect aio writes properly here..
>>
>> Could we just change percpu_rw_semaphore->read_count to be a signed
>> integer? The down_write path sums up the counters from all cpus...
>
> To what point?
Duh, nevermind. You're right, it should work as-is.
-Jeff
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