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Commit c32ccd87 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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[PATCH] inotify: lock avoidance with parent watch status in dentry 



Previous inotify work avoidance is good when inotify is completely unused,
but it breaks down if even a single watch is in place anywhere in the
system.  Robin Holt notices that udev is one such culprit - it slows down a
512-thread application on a 512 CPU system from 6 seconds to 22 minutes.

Solve this by adding a flag in the dentry that tells inotify whether or not
its parent inode has a watch on it.  Event queueing to parent will skip
taking locks if this flag is cleared.  Setting and clearing of this flag on
all child dentries versus event delivery: this is no in terms of race
cases, and that was shown to be equivalent to always performing the check.

The essential behaviour is that activity occuring _after_ a watch has been
added and _before_ it has been removed, will generate events.

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Cc: Robert Love <rml@novell.com>
Cc: John McCutchan <ttb@tentacle.dhs.org>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent bf36b901

fs/dcache.c

+8 −0
Original line number Diff line number Diff line
@@ -802,6 +802,7 @@ void d_instantiate(struct dentry *entry, struct inode * inode) 
	if (inode)

		list_add(&entry->d_alias, &inode->i_dentry);

	entry->d_inode = inode;

	fsnotify_d_instantiate(entry, inode);

	spin_unlock(&dcache_lock);

	security_d_instantiate(entry, inode);

}
@@ -853,6 +854,7 @@ struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode) 
	list_add(&entry->d_alias, &inode->i_dentry);

do_negative:

	entry->d_inode = inode;

	fsnotify_d_instantiate(entry, inode);

	spin_unlock(&dcache_lock);

	security_d_instantiate(entry, inode);

	return NULL;
@@ -983,6 +985,7 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry) 
		new = __d_find_alias(inode, 1);

		if (new) {

			BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));

			fsnotify_d_instantiate(new, inode);

			spin_unlock(&dcache_lock);

			security_d_instantiate(new, inode);

			d_rehash(dentry);
@@ -992,6 +995,7 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry) 
			/* d_instantiate takes dcache_lock, so we do it by hand */

			list_add(&dentry->d_alias, &inode->i_dentry);

			dentry->d_inode = inode;

			fsnotify_d_instantiate(dentry, inode);

			spin_unlock(&dcache_lock);

			security_d_instantiate(dentry, inode);

			d_rehash(dentry);
@@ -1176,6 +1180,9 @@ void d_delete(struct dentry * dentry) 
	spin_lock(&dentry->d_lock);

	isdir = S_ISDIR(dentry->d_inode->i_mode);

	if (atomic_read(&dentry->d_count) == 1) {

		/* remove this and other inotify debug checks after 2.6.18 */

		dentry->d_flags &= ~DCACHE_INOTIFY_PARENT_WATCHED;



		dentry_iput(dentry);

		fsnotify_nameremove(dentry, isdir);

		return;
@@ -1342,6 +1349,7 @@ void d_move(struct dentry * dentry, struct dentry * target) 


	list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);

	spin_unlock(&target->d_lock);

	fsnotify_d_move(dentry);

	spin_unlock(&dentry->d_lock);

	write_sequnlock(&rename_lock);

	spin_unlock(&dcache_lock);

fs/inotify.c

+77 −10
Original line number Diff line number Diff line
@@ -38,7 +38,6 @@ 
#include <asm/ioctls.h>



static atomic_t inotify_cookie;

static atomic_t inotify_watches;



static kmem_cache_t *watch_cachep;

static kmem_cache_t *event_cachep;
@@ -380,6 +379,48 @@ static int find_inode(const char __user *dirname, struct nameidata *nd, 
	return error;

}



/*

 * inotify_inode_watched - returns nonzero if there are watches on this inode

 * and zero otherwise.  We call this lockless, we do not care if we race.

 */

static inline int inotify_inode_watched(struct inode *inode)

{

	return !list_empty(&inode->inotify_watches);

}



/*

 * Get child dentry flag into synch with parent inode.

 * Flag should always be clear for negative dentrys.

 */

static void set_dentry_child_flags(struct inode *inode, int watched)

{

	struct dentry *alias;



	spin_lock(&dcache_lock);

	list_for_each_entry(alias, &inode->i_dentry, d_alias) {

		struct dentry *child;



		list_for_each_entry(child, &alias->d_subdirs, d_u.d_child) {

			if (!child->d_inode) {

				WARN_ON(child->d_flags & DCACHE_INOTIFY_PARENT_WATCHED);

				continue;

			}

			spin_lock(&child->d_lock);

			if (watched) {

				WARN_ON(child->d_flags &

						DCACHE_INOTIFY_PARENT_WATCHED);

				child->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;

			} else {

				WARN_ON(!(child->d_flags &

					DCACHE_INOTIFY_PARENT_WATCHED));

				child->d_flags&=~DCACHE_INOTIFY_PARENT_WATCHED;

			}

			spin_unlock(&child->d_lock);

		}

	}

	spin_unlock(&dcache_lock);

}



/*

 * create_watch - creates a watch on the given device.

 *
@@ -426,7 +467,6 @@ static struct inotify_watch *create_watch(struct inotify_device *dev, 
	get_inotify_watch(watch);



	atomic_inc(&dev->user->inotify_watches);

	atomic_inc(&inotify_watches);



	return watch;

}
@@ -458,8 +498,10 @@ static void remove_watch_no_event(struct inotify_watch *watch, 
	list_del(&watch->i_list);

	list_del(&watch->d_list);



	if (!inotify_inode_watched(watch->inode))

		set_dentry_child_flags(watch->inode, 0);



	atomic_dec(&dev->user->inotify_watches);

	atomic_dec(&inotify_watches);

	idr_remove(&dev->idr, watch->wd);

	put_inotify_watch(watch);

}
@@ -481,16 +523,39 @@ static void remove_watch(struct inotify_watch *watch,struct inotify_device *dev) 
	remove_watch_no_event(watch, dev);

}



/* Kernel API */



/*

 * inotify_inode_watched - returns nonzero if there are watches on this inode

 * and zero otherwise.  We call this lockless, we do not care if we race.

 * inotify_d_instantiate - instantiate dcache entry for inode

 */

static inline int inotify_inode_watched(struct inode *inode)

void inotify_d_instantiate(struct dentry *entry, struct inode *inode)

{

	return !list_empty(&inode->inotify_watches);

	struct dentry *parent;



	if (!inode)

		return;



	WARN_ON(entry->d_flags & DCACHE_INOTIFY_PARENT_WATCHED);

	spin_lock(&entry->d_lock);

	parent = entry->d_parent;

	if (inotify_inode_watched(parent->d_inode))

		entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;

	spin_unlock(&entry->d_lock);

}



/* Kernel API */

/*

 * inotify_d_move - dcache entry has been moved

 */

void inotify_d_move(struct dentry *entry)

{

	struct dentry *parent;



	parent = entry->d_parent;

	if (inotify_inode_watched(parent->d_inode))

		entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;

	else

		entry->d_flags &= ~DCACHE_INOTIFY_PARENT_WATCHED;

}



/**

 * inotify_inode_queue_event - queue an event to all watches on this inode
@@ -538,7 +603,7 @@ void inotify_dentry_parent_queue_event(struct dentry *dentry, u32 mask, 
	struct dentry *parent;

	struct inode *inode;



	if (!atomic_read (&inotify_watches))

	if (!(dentry->d_flags & DCACHE_INOTIFY_PARENT_WATCHED))

		return;



	spin_lock(&dentry->d_lock);
@@ -993,6 +1058,9 @@ asmlinkage long sys_inotify_add_watch(int fd, const char __user *path, u32 mask) 
		goto out;

	}



	if (!inotify_inode_watched(inode))

		set_dentry_child_flags(inode, 1);



	/* Add the watch to the device's and the inode's list */

	list_add(&watch->d_list, &dev->watches);

	list_add(&watch->i_list, &inode->inotify_watches);
@@ -1065,7 +1133,6 @@ static int __init inotify_setup(void) 
	inotify_max_user_watches = 8192;



	atomic_set(&inotify_cookie, 0);

	atomic_set(&inotify_watches, 0);



	watch_cachep = kmem_cache_create("inotify_watch_cache",

					 sizeof(struct inotify_watch),

include/linux/dcache.h

+2 −0
Original line number Diff line number Diff line
@@ -162,6 +162,8 @@ d_iput: no no no yes 
#define DCACHE_REFERENCED	0x0008  /* Recently used, don't discard. */

#define DCACHE_UNHASHED		0x0010	



#define DCACHE_INOTIFY_PARENT_WATCHED	0x0020 /* Parent inode is watched */



extern spinlock_t dcache_lock;



/**

include/linux/fsnotify.h

+19 −0
Original line number Diff line number Diff line
@@ -16,6 +16,25 @@ 
#include <linux/dnotify.h>

#include <linux/inotify.h>



/*

 * fsnotify_d_instantiate - instantiate a dentry for inode

 * Called with dcache_lock held.

 */

static inline void fsnotify_d_instantiate(struct dentry *entry,

						struct inode *inode)

{

	inotify_d_instantiate(entry, inode);

}



/*

 * fsnotify_d_move - entry has been moved

 * Called with dcache_lock and entry->d_lock held.

 */

static inline void fsnotify_d_move(struct dentry *entry)

{

	inotify_d_move(entry);

}



/*

 * fsnotify_move - file old_name at old_dir was moved to new_name at new_dir

 */

include/linux/inotify.h

+11 −0
Original line number Diff line number Diff line
@@ -71,6 +71,8 @@ struct inotify_event { 


#ifdef CONFIG_INOTIFY



extern void inotify_d_instantiate(struct dentry *, struct inode *);

extern void inotify_d_move(struct dentry *);

extern void inotify_inode_queue_event(struct inode *, __u32, __u32,

				      const char *);

extern void inotify_dentry_parent_queue_event(struct dentry *, __u32, __u32,
@@ -81,6 +83,15 @@ extern u32 inotify_get_cookie(void); 


#else



static inline void inotify_d_instantiate(struct dentry *dentry,

					struct inode *inode)

{

}



static inline void inotify_d_move(struct dentry *dentry)

{

}



static inline void inotify_inode_queue_event(struct inode *inode,

					     __u32 mask, __u32 cookie,

					     const char *filename)