Li Zefan wrote:
> Al Viro wrote:
>> On Fri, Feb 13, 2009 at 06:41:35AM +0000, Al Viro wrote:
>>
>> Aaaargh...
>>
>> /*
>> * We don't have to hold all of the locks at the
>> * same time here because we know that we're the
>> * last reference to mnt and that no new writers
>> * can come in.
>> */
>> for_each_possible_cpu(cpu) {
>> struct mnt_writer *cpu_writer = &per_cpu(mnt_writers, cpu);
>> if (cpu_writer->mnt != mnt)
>> continue;
>> spin_lock(&cpu_writer->lock);
>>
>> is *almost* OK. Modulo SMP cache coherency. We know that nothing should
>> be setting ->mnt to ours anymore, that's fine. But we do not know if
>> we'd seen *earlier* change done on CPU in question (not the one we
>> are running __mntput() on).
>>
>> I probably would still like to use milder solution in the long run, but for
>> now let's check if turning that into
>>
>> struct mnt_writer *cpu_writer = &per_cpu(mnt_writers, cpu);
>> spin_lock(&cpu_writer->lock);
>> if (cpu_writer->mnt != mnt) {
>> spin_unlock(&cpu_writer->lock);
>> continue;
>> }
>> prevents the problem, OK?
>>
>
> Sure, I'll try. :)
>
Not a single warning for the whole weekend, so I think above change works.
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