dentry_kill(): don't try to remove from shrink list

If the victim in on the shrink list, don't remove it from there.
If shrink_dentry_list() manages to remove it from the list before
we are done - fine, we'll just free it as usual.  If not - mark
it with new flag (DCACHE_MAY_FREE) and leave it there.

Eventually, shrink_dentry_list() will get to it, remove the sucker
from shrink list and call dentry_kill(dentry, 0).  Which is where
we'll deal with freeing.

Since now dentry_kill(dentry, 0) may happen after or during
dentry_kill(dentry, 1), we need to recognize that (by seeing
DCACHE_DENTRY_KILLED already set), unlock everything
and either free the sucker (in case DCACHE_MAY_FREE has been
set) or leave it for ongoing dentry_kill(dentry, 1) to deal with.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 21 insertions, 8 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index e482775343a0..58e26bee7ef4 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -468,7 +468,14 @@ dentry_kill(struct dentry *dentry, int unlock_on_failure)
         __releases(dentry->d_lock)
 {
         struct inode *inode;
-        struct dentry *parent;
+        struct dentry *parent = NULL;
+        bool can_free = true;
+
+        if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
+                can_free = dentry->d_flags & DCACHE_MAY_FREE;
+                spin_unlock(&dentry->d_lock);
+                goto out;
+        }
 
         inode = dentry->d_inode;
         if (inode && !spin_trylock(&inode->i_lock)) {
@@ -479,9 +486,7 @@ relock:
                 }
                 return dentry; /* try again with same dentry */
         }
-        if (IS_ROOT(dentry))
-                parent = NULL;
-        else
+        if (!IS_ROOT(dentry))
                 parent = dentry->d_parent;
         if (parent && !spin_trylock(&parent->d_lock)) {
                 if (inode)
@@ -504,8 +509,6 @@ relock:
         if (dentry->d_flags & DCACHE_LRU_LIST) {
                 if (!(dentry->d_flags & DCACHE_SHRINK_LIST))
                         d_lru_del(dentry);
-                else
-                        d_shrink_del(dentry);
         }
         /* if it was on the hash then remove it */
         __d_drop(dentry);
@@ -527,7 +530,15 @@ relock:
         if (dentry->d_op && dentry->d_op->d_release)
                 dentry->d_op->d_release(dentry);
 
-        dentry_free(dentry);
+        spin_lock(&dentry->d_lock);
+        if (dentry->d_flags & DCACHE_SHRINK_LIST) {
+                dentry->d_flags |= DCACHE_MAY_FREE;
+                can_free = false;
+        }
+        spin_unlock(&dentry->d_lock);
+out:
+        if (likely(can_free))
+                dentry_free(dentry);
         return parent;
 }
 
@@ -829,7 +840,7 @@ static void shrink_dentry_list(struct list_head *list)
                  * We found an inuse dentry which was not removed from
                  * the LRU because of laziness during lookup. Do not free it.
                  */
-                if (dentry->d_lockref.count) {
+                if ((int)dentry->d_lockref.count > 0) {
                         spin_unlock(&dentry->d_lock);
                         continue;
                 }
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 3b9bfdb83ba6..3c7ec327ebd2 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -221,6 +221,8 @@ struct dentry_operations {
 #define DCACHE_SYMLINK_TYPE             0x00300000 /* Symlink */
 #define DCACHE_FILE_TYPE                0x00400000 /* Other file type */
 
+#define DCACHE_MAY_FREE                 0x00800000
+
 extern seqlock_t rename_lock;
 
 static inline int dname_external(const struct dentry *dentry)