On Wed, Apr 30, 2014 at 08:42:01PM +0200, Miklos Szeredi wrote:
> Message-ID: <20140430154958.GC3113@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
I see... Several points:
* I still think that it's better to do handling of "we see
DCACHE_DENTRY_KILLED already set" in dentry_kill() itself.
* in dentry_kill(dentry, 0) we *know* that it's not on a shrink
list - the caller has just removed it from there and we'd kept ->d_lock
since that point. What's more, with that scheme we don't need to bother
with can_free at all - just grab ->d_lock after ->d_release() call and check
DCACHE_SHRINK_LIST. No sense trying to avoid that - in case where we
could just go ahead and free the sucker, there's neither contention nor
anybody else interested in that cacheline, so spin_lock(&dentry->d_lock)
is pretty much free.
IOW, I'd prefer to do the following (completely untested) on top of 1/6--4/6:
diff --git a/fs/dcache.c b/fs/dcache.c
index e482775..82d8eb4 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -489,6 +489,17 @@ relock:
goto relock;
}
+ if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
+ if (parent)
+ spin_unlock(&parent->d_lock);
+ if (dentry->d_flags & DCACHE_MAY_FREE) {
+ spin_unlock(&dentry->d_lock);
+ dentry_free(dentry);
+ } else {
+ spin_unlock(&dentry->d_lock);
+ }
+ return parent;
+ }
/*
* The dentry is now unrecoverably dead to the world.
*/
@@ -504,8 +515,6 @@ 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 +536,14 @@ 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;
+ spin_unlock(&dentry->d_lock);
+ } else {
+ spin_unlock(&dentry->d_lock);
+ dentry_free(dentry);
+ }
return parent;
}
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 3b9bfdb..3c7ec32 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)
--
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