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SubjectRe: [Q] missing unused dentry in prune_dcache()?
Date
Vasily Averin <vvs@sw.ru> wrote:

> I've noticed one more minor issue in your patch: in
> shrink_dcache_for_umount_subtree() function you decrement
> dentry_stat.nr_dentry without dcache_lock.

How about the attached patch?

David
---
VFS: Fix an error in unused dentry counting

From: David Howells <dhowells@redhat.com>

Fix an error in unused dentry counting in shrink_dcache_for_umount_subtree() in
which the count is modified without the dcache_lock held.

Signed-Off-By: David Howells <dhowells@redhat.com>
---

fs/dcache.c | 22 +++++++++++++++-------
1 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index a1ff91e..eab1bf4 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -553,16 +553,17 @@ repeat:
* - see the comments on shrink_dcache_for_umount() for a description of the
* locking
*/
-static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
+static unsigned shrink_dcache_for_umount_subtree(struct dentry *dentry)
{
struct dentry *parent;
+ unsigned detached = 0;

BUG_ON(!IS_ROOT(dentry));

/* detach this root from the system */
spin_lock(&dcache_lock);
if (!list_empty(&dentry->d_lru)) {
- dentry_stat.nr_unused--;
+ detached++;
list_del_init(&dentry->d_lru);
}
__d_drop(dentry);
@@ -579,7 +580,7 @@ static void shrink_dcache_for_umount_sub
list_for_each_entry(loop, &dentry->d_subdirs,
d_u.d_child) {
if (!list_empty(&loop->d_lru)) {
- dentry_stat.nr_unused--;
+ detached++;
list_del_init(&loop->d_lru);
}

@@ -620,7 +621,7 @@ static void shrink_dcache_for_umount_sub
atomic_dec(&parent->d_count);

list_del(&dentry->d_u.d_child);
- dentry_stat.nr_dentry--; /* For d_free, below */
+ detached++; /* For d_free, below */

inode = dentry->d_inode;
if (inode) {
@@ -638,7 +639,7 @@ static void shrink_dcache_for_umount_sub
* otherwise we ascend to the parent and move to the
* next sibling if there is one */
if (!parent)
- return;
+ return detached;

dentry = parent;

@@ -663,6 +664,7 @@ static void shrink_dcache_for_umount_sub
void shrink_dcache_for_umount(struct super_block *sb)
{
struct dentry *dentry;
+ unsigned detached = 0;

if (down_read_trylock(&sb->s_umount))
BUG();
@@ -670,11 +672,17 @@ void shrink_dcache_for_umount(struct sup
dentry = sb->s_root;
sb->s_root = NULL;
atomic_dec(&dentry->d_count);
- shrink_dcache_for_umount_subtree(dentry);
+ detached = shrink_dcache_for_umount_subtree(dentry);

while (!hlist_empty(&sb->s_anon)) {
dentry = hlist_entry(sb->s_anon.first, struct dentry, d_hash);
- shrink_dcache_for_umount_subtree(dentry);
+ detached += shrink_dcache_for_umount_subtree(dentry);
+ }
+
+ if (detached) {
+ spin_lock(&dcache_lock);
+ dentry_stat.nr_unused -= detached;
+ spin_unlock(&dcache_lock);
}
}

-
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