From: Ian Kent <[email protected]>
The locking for the list traversal in get_next_positive_subdir() is
wrong, so fix it.
Signed-off-by: Ian Kent <[email protected]>
---
fs/autofs4/expire.c | 10 ++++++----
1 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index 1feb68e..20cc9fd 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -97,9 +97,9 @@ static struct dentry *get_next_positive_subdir(struct dentry *prev,
struct dentry *p, *q;
spin_lock(&sbi->lookup_lock);
+ spin_lock(&root->d_lock);
if (prev == NULL) {
- spin_lock(&root->d_lock);
prev = dget_dlock(root);
next = prev->d_subdirs.next;
p = prev;
@@ -107,12 +107,13 @@ static struct dentry *get_next_positive_subdir(struct dentry *prev,
}
p = prev;
- spin_lock(&p->d_lock);
+ spin_lock_nested(&p->d_lock, DENTRY_D_LOCK_NESTED);
again:
next = p->d_u.d_child.next;
start:
if (next == &root->d_subdirs) {
spin_unlock(&p->d_lock);
+ spin_unlock(&root->d_lock);
spin_unlock(&sbi->lookup_lock);
dput(prev);
return NULL;
@@ -121,8 +122,8 @@ start:
q = list_entry(next, struct dentry, d_u.d_child);
spin_lock_nested(&q->d_lock, DENTRY_D_LOCK_NESTED);
- /* Negative dentry - try next */
- if (!simple_positive(q)) {
+ /* Negative dentry or already gone - try next */
+ if (q->d_count == 0 || !simple_positive(q)) {
spin_unlock(&p->d_lock);
lock_set_subclass(&q->d_lock.dep_map, 0, _RET_IP_);
p = q;
@@ -131,6 +132,7 @@ start:
dget_dlock(q);
spin_unlock(&q->d_lock);
spin_unlock(&p->d_lock);
+ spin_unlock(&root->d_lock);
spin_unlock(&sbi->lookup_lock);
dput(prev);
On Tue, May 22, 2012 at 7:49 PM, Ian Kent <[email protected]> wrote:
>
> The locking for the list traversal in get_next_positive_subdir() is
> wrong, so fix it.
As an explanation, this kind of thing is totally useless. It doesn't
actually give any information at all. It's like saying "change
locking"
What happened, and why? Why is the new nested spinlock ok and won't
deadlock against other nested users? Wazzup?
Linus
On Tue, 2012-05-22 at 19:53 -0700, Linus Torvalds wrote:
> On Tue, May 22, 2012 at 7:49 PM, Ian Kent <[email protected]> wrote:
> >
> > The locking for the list traversal in get_next_positive_subdir() is
> > wrong, so fix it.
>
> As an explanation, this kind of thing is totally useless. It doesn't
> actually give any information at all. It's like saying "change
> locking"
OK, I'll fix that and re-submit.
Ian
On Tue, 2012-05-22 at 19:53 -0700, Linus Torvalds wrote:
> On Tue, May 22, 2012 at 7:49 PM, Ian Kent <[email protected]> wrote:
> >
> > The locking for the list traversal in get_next_positive_subdir() is
> > wrong, so fix it.
>
> As an explanation, this kind of thing is totally useless. It doesn't
> actually give any information at all. It's like saying "change
> locking"
>
> What happened, and why? Why is the new nested spinlock ok and won't
> deadlock against other nested users? Wazzup?
It's good that you questioned this Linus.
Looking again at dput() I think the traversal still isn't quite right.
For a start the test for d_count 0 or positive and hashed can never be
true since the point of the change was to take the d_lock of the
d_subdirs dentry for the traversal.
I'll need to work on this some more, thanks.
Ian
On Wed, 2012-05-23 at 15:22 +0800, Ian Kent wrote:
> On Tue, 2012-05-22 at 19:53 -0700, Linus Torvalds wrote:
> > On Tue, May 22, 2012 at 7:49 PM, Ian Kent <[email protected]> wrote:
> > >
> > > The locking for the list traversal in get_next_positive_subdir() is
> > > wrong, so fix it.
> >
> > As an explanation, this kind of thing is totally useless. It doesn't
> > actually give any information at all. It's like saying "change
> > locking"
> >
> > What happened, and why? Why is the new nested spinlock ok and won't
> > deadlock against other nested users? Wazzup?
>
> It's good that you questioned this Linus.
>
> Looking again at dput() I think the traversal still isn't quite right.
>
> For a start the test for d_count 0 or positive and hashed can never be
Correction, that second check is actually !(positive and hashed) in the
code.
> true since the point of the change was to take the d_lock of the
> d_subdirs dentry for the traversal.
>
> I'll need to work on this some more, thanks.
> Ian
On Wed, 2012-05-23 at 15:30 +0800, Ian Kent wrote:
> On Wed, 2012-05-23 at 15:22 +0800, Ian Kent wrote:
> > On Tue, 2012-05-22 at 19:53 -0700, Linus Torvalds wrote:
> > > On Tue, May 22, 2012 at 7:49 PM, Ian Kent <[email protected]> wrote:
> > > >
> > > > The locking for the list traversal in get_next_positive_subdir() is
> > > > wrong, so fix it.
> > >
> > > As an explanation, this kind of thing is totally useless. It doesn't
> > > actually give any information at all. It's like saying "change
> > > locking"
> > >
> > > What happened, and why? Why is the new nested spinlock ok and won't
> > > deadlock against other nested users? Wazzup?
> >
> > It's good that you questioned this Linus.
> >
> > Looking again at dput() I think the traversal still isn't quite right.
> >
> > For a start the test for d_count 0 or positive and hashed can never be
>
> Correction, that second check is actually !(positive and hashed) in the
> code.
>
> > true since the point of the change was to take the d_lock of the
> > d_subdirs dentry for the traversal.
That's not right, ignore this.
> >
> > I'll need to work on this some more, thanks.
> > Ian
>