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SubjectRe: [PATCH 3/3] VFS: close race between getcwd() and d_move()
On Tue, Nov 21 2017, Al Viro wrote:

> On Fri, Nov 10, 2017 at 08:53:28PM +0000, Al Viro wrote:
>> On Fri, Nov 10, 2017 at 03:45:41PM +1100, NeilBrown wrote:
>> > -void __d_drop(struct dentry *dentry)
>> > +static void ___d_drop(struct dentry *dentry)
>> > {
>> > if (!d_unhashed(dentry)) {
>> > struct hlist_bl_head *b;
>> > @@ -486,12 +488,15 @@ void __d_drop(struct dentry *dentry)
>> >
>> > hlist_bl_lock(b);
>> > __hlist_bl_del(&dentry->d_hash);
>> > - dentry->d_hash.pprev = NULL;
>> > hlist_bl_unlock(b);
>> > /* After this call, in-progress rcu-walk path lookup will fail. */
>> > write_seqcount_invalidate(&dentry->d_seq);
>> > }
>> > }
>> > +void __d_drop(struct dentry *dentry) {
>> > + ___d_drop(dentry);
>> > + dentry->d_hash.pprev = NULL;
>>
>> Umm... That reordering (unhashed vs. ->d_seq) might be a problem
>> on the RCU side. I'm not sure it is, we might get away with that,
>> actually, but I want to finish digging through the pathwalk-related
>> code. Cursing it for being too subtle for its own good, as usual...
>
> OK, I believe that it's survivable, but I'd prefer to keep in -next
> for a while and give it more testing.

Great, thanks. I assume you will fix the silly '{' at the end of the
line when defining __d_drop(). Let me know if you would rather I
resend.

Thanks,
NeilBrown
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