Messages in this thread | | | Subject | Re: [PATCH 6/6] autofs4: don't take spinlock when not needed in autofs4_lookup_expiring | From | Ian Kent <> | Date | Wed, 16 Jul 2014 11:42:12 +0800 |
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On Thu, 2014-07-10 at 09:41 +1000, NeilBrown wrote: > If the expiring_list is empty, we can avoid a costly spinlock > in the rcu-walk path through authfs4_d_manage. > > Signed-off-by: NeilBrown <neilb@suse.de>
I know it should be straight forward to say this is OK but I always think twice and again about areas that are subject to race pressure, such as the expire to mount pressure of this code.
After thinking about it for a while now I don't have any reason to think this would be a problem. Perhaps later pressure testing will reveal something I missed.
It occurs to me that autofs4_lookup_active() might benefit from a similar addition. Multiple calls to ->lookup() made while the dentry is still unhashed should have enforced ordering due to the directory i_mutex so there shouldn't be a problem adding this. But perhaps you haven't seen delays in that function.
Acked-by: Ian Kent <raven@themaw.net>
> --- > fs/autofs4/root.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c > index 1ad119407e2f..774c2dab331b 100644 > --- a/fs/autofs4/root.c > +++ b/fs/autofs4/root.c > @@ -219,6 +219,8 @@ static struct dentry *autofs4_lookup_expiring(struct dentry *dentry, > const unsigned char *str = name->name; > struct list_head *p, *head; > > + if (list_empty(&sbi->expiring_list)) > + return NULL; > spin_lock(&sbi->lookup_lock); > head = &sbi->expiring_list; > list_for_each(p, head) { > >
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