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>>No, it looks as it is not :(>>Have you noticed my comment about "count" argument to prune_dcache()?
>>For example, prune_dcache() is called from shrink_dcache_parent() which
>>is called in many places and not all of them have PF_MEMALLOC or
>>s_umount semaphore for write. But prune_dcache() doesn't care for super
>>blocks etc. It simply shrinks N dentries which are found _first_.
>>
>>So the condition:
>>+ if ((current->flags & PF_MEMALLOC) &&
>>+ !(ret = down_read_trylock(&s->s_umount))) {
>>is not always true when the race occurs, as PF_MEMALLOC is not always set.> > > I understand your comment about shrink_dcache_parent() being called
> from several places. prune_one_dentry() would eventually dput the parent,
> but unmount would go ahead and unmount the filesystem before the
> dput of the parent could happen.
exactly.
> Given that background, I thought our main concern was with respect to
> unmount. The race was between shrink_dcache_parent() (called from unmount)
> and shrink_dcache_memory() (called from the allocator), hence the fix
> for the race condition.
Partial fix doesn't make much sense from my point of view.
> I just noticied that 2.6.16-rc* now seems to have drop_slab() where
> PF_MEMALLOC is not set. So, we can still race with my fix if there
> if /proc/sys/vm/drop_caches is written to and unmount is done in parallel.
> > A simple hack would be to set PF_MEMALLOC in drop_slab(), but I do not
> think it is a good idea.
Yeah, playing with PF_MEMALLOC can be not so good idea :/
And as it doesn't help in other cases it looks unpromising...
>>>Have you had any other feedback on this?>>here it is :)> Thanks for your detailed feedback
Sorry, that I did it too late :/
Thanks,
Kirill
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