VFS: Remove dentry->d_lock locking from shrink_dcache_for_umount_subtree()
Locks of the dcache_lock were replaced by locks of dentry->d_lock in commits such as:2304450783
2fd6b7f507
as part of the RCU-based pathwalk changes, despite the fact that the caller (shrink_dcache_for_umount()) notes in the banner comment the reasons that d_lock is not necessary in these functions: /* * destroy the dentries attached to a superblock on unmounting * - we don't need to use dentry->d_lock because: * - the superblock is detached from all mountings and open files, so the * dentry trees will not be rearranged by the VFS * - s_umount is write-locked, so the memory pressure shrinker will ignore * any dentries belonging to this superblock that it comes across * - the filesystem itself is no longer permitted to rearrange the dentries * in this superblock */ So remove these locks. If the locks are actually necessary, then this banner comment should be altered instead. The hash table chains are protected by 1-bit locks in the hash table heads, so those shouldn't be a problem. Note that to make this work, __d_drop() has to be split so that the RCUwalk barrier can be avoided. This causes problems otherwise as it has an assertion that dentry->d_lock is locked - but there is no need for that as no one else can be trying to access this dentry, except to step over it (and that should be handled by d_free(), I think). Signed-off-by: David Howells <dhowells@redhat.com> Cc: Nick Piggin <npiggin@kernel.dk> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
parent
35f40ef002
commit
c6627c60c0
48
fs/dcache.c
48
fs/dcache.c
@ -301,6 +301,27 @@ static struct dentry *d_kill(struct dentry *dentry, struct dentry *parent)
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return parent;
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return parent;
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}
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}
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/*
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* Unhash a dentry without inserting an RCU walk barrier or checking that
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* dentry->d_lock is locked. The caller must take care of that, if
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* appropriate.
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*/
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static void __d_shrink(struct dentry *dentry)
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{
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if (!d_unhashed(dentry)) {
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struct hlist_bl_head *b;
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if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
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b = &dentry->d_sb->s_anon;
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else
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b = d_hash(dentry->d_parent, dentry->d_name.hash);
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hlist_bl_lock(b);
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__hlist_bl_del(&dentry->d_hash);
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dentry->d_hash.pprev = NULL;
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hlist_bl_unlock(b);
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}
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}
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/**
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/**
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* d_drop - drop a dentry
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* d_drop - drop a dentry
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* @dentry: dentry to drop
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* @dentry: dentry to drop
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@ -319,17 +340,7 @@ static struct dentry *d_kill(struct dentry *dentry, struct dentry *parent)
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void __d_drop(struct dentry *dentry)
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void __d_drop(struct dentry *dentry)
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{
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{
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if (!d_unhashed(dentry)) {
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if (!d_unhashed(dentry)) {
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struct hlist_bl_head *b;
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__d_shrink(dentry);
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if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
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b = &dentry->d_sb->s_anon;
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else
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b = d_hash(dentry->d_parent, dentry->d_name.hash);
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hlist_bl_lock(b);
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__hlist_bl_del(&dentry->d_hash);
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dentry->d_hash.pprev = NULL;
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hlist_bl_unlock(b);
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dentry_rcuwalk_barrier(dentry);
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dentry_rcuwalk_barrier(dentry);
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}
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}
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}
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}
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@ -832,10 +843,8 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
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BUG_ON(!IS_ROOT(dentry));
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BUG_ON(!IS_ROOT(dentry));
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/* detach this root from the system */
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/* detach this root from the system */
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spin_lock(&dentry->d_lock);
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dentry_lru_del(dentry);
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dentry_lru_del(dentry);
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__d_drop(dentry);
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__d_shrink(dentry);
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spin_unlock(&dentry->d_lock);
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for (;;) {
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for (;;) {
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/* descend to the first leaf in the current subtree */
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/* descend to the first leaf in the current subtree */
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@ -844,16 +853,11 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
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/* this is a branch with children - detach all of them
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/* this is a branch with children - detach all of them
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* from the system in one go */
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* from the system in one go */
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spin_lock(&dentry->d_lock);
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list_for_each_entry(loop, &dentry->d_subdirs,
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list_for_each_entry(loop, &dentry->d_subdirs,
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d_u.d_child) {
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d_u.d_child) {
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spin_lock_nested(&loop->d_lock,
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DENTRY_D_LOCK_NESTED);
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dentry_lru_del(loop);
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dentry_lru_del(loop);
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__d_drop(loop);
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__d_shrink(loop);
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spin_unlock(&loop->d_lock);
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}
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}
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spin_unlock(&dentry->d_lock);
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/* move to the first child */
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/* move to the first child */
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dentry = list_entry(dentry->d_subdirs.next,
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dentry = list_entry(dentry->d_subdirs.next,
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@ -885,10 +889,8 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
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list_del(&dentry->d_u.d_child);
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list_del(&dentry->d_u.d_child);
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} else {
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} else {
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parent = dentry->d_parent;
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parent = dentry->d_parent;
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spin_lock(&parent->d_lock);
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parent->d_count--;
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parent->d_count--;
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list_del(&dentry->d_u.d_child);
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list_del(&dentry->d_u.d_child);
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spin_unlock(&parent->d_lock);
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}
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}
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inode = dentry->d_inode;
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inode = dentry->d_inode;
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@ -935,9 +937,7 @@ void shrink_dcache_for_umount(struct super_block *sb)
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dentry = sb->s_root;
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dentry = sb->s_root;
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sb->s_root = NULL;
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sb->s_root = NULL;
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spin_lock(&dentry->d_lock);
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dentry->d_count--;
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dentry->d_count--;
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spin_unlock(&dentry->d_lock);
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shrink_dcache_for_umount_subtree(dentry);
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shrink_dcache_for_umount_subtree(dentry);
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while (!hlist_bl_empty(&sb->s_anon)) {
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while (!hlist_bl_empty(&sb->s_anon)) {
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