Messages in this thread Patch in this message | | | Date | Mon, 30 Jan 2006 13:03:18 +0100 | From | Jan Blunck <> | Subject | Re: [PATCH] shrink_dcache_parent() races against shrink_dcache_memory() |
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On Mon, Jan 23, Kirill Korotaev wrote:
> 1. this patch doesn't fix the whole problem. iput() after sb free is > still possible. So busy inodes after umount too. > 2. it has big problems with locking... >
Uh yeah! I fixed the second issue but since the patch doesnt helped and only gots the reference counting a little bit cleaner I don't post it.
> comments below inside. >
New patch attached below. Comments are welcome.
Regards, Jan
-- Jan Blunck jblunck@suse.de SuSE LINUX AG - A Novell company Maxfeldstr. 5 +49-911-74053-608 D-90409 Nürnberg http://www.suse.de From: Jan Blunck <jblunck@suse.de> Subject: Fix shrink_dcache_parent() against shrink_dcache_memory() race References: 136310
Kirill Korotaev <dev@sw.ru> discovered a race between shrink_dcache_parent() and shrink_dcache_memory() which leads to "Busy inodes after unmount". When unmounting a file system shrink_dcache_parent() is racing against a possible shrink_dcache_memory(). This might lead to the situation that shrink_dcache_parent() is returning too early. In this situation the super_block is destroyed before shrink_dcache_memory() could put the inode.
This patch fixes the problem through introducing a prunes counter which is incremented when a dentry is pruned but the corresponding inoded isn't put yet. When the prunes counter is not null, shrink_dcache_parent() is waiting and restarting its work.
Signed-off-by: Jan Blunck <jblunck@suse.de>
---
fs/dcache.c | 36 ++++++++++++++++++++++++++++++++++++ fs/super.c | 4 +++- include/linux/fs.h | 3 +++ 3 files changed, 42 insertions(+), 1 deletion(-)
Index: linux-2.6/fs/dcache.c =================================================================== --- linux-2.6.orig/fs/dcache.c +++ linux-2.6/fs/dcache.c @@ -364,17 +364,21 @@ restart: */ static inline void prune_one_dentry(struct dentry * dentry) { + struct super_block *sb = dentry->d_sb; struct dentry * parent; __d_drop(dentry); list_del(&dentry->d_u.d_child); dentry_stat.nr_dentry--; /* For d_free, below */ + sb->s_prunes++; dentry_iput(dentry); parent = dentry->d_parent; d_free(dentry); if (parent != dentry) dput(parent); spin_lock(&dcache_lock); + sb->s_prunes--; + wake_up(&sb->s_wait_prunes); } /** @@ -623,6 +627,34 @@ out: return found; } +static int wait_on_prunes(struct super_block *sb) +{ + DEFINE_WAIT(wait); + + spin_lock(&dcache_lock); + if (!sb->s_prunes) { + spin_unlock(&dcache_lock); + return 0; + } + + printk(KERN_DEBUG "%s: waiting for %d prunes\n", __FUNCTION__, + sb->s_prunes); + + while (1) { + prepare_to_wait(&sb->s_wait_prunes, &wait, + TASK_UNINTERRUPTIBLE); + if (!sb->s_prunes) + break; + spin_unlock(&dcache_lock); + schedule(); + spin_lock(&dcache_lock); + } + + finish_wait(&sb->s_wait_prunes, &wait); + spin_unlock(&dcache_lock); + return 1; +} + /** * shrink_dcache_parent - prune dcache * @parent: parent of entries to prune @@ -634,8 +666,12 @@ void shrink_dcache_parent(struct dentry { int found; + again: while ((found = select_parent(parent)) != 0) prune_dcache(found); + + if (wait_on_prunes(parent->d_sb)) + goto again; } /** Index: linux-2.6/fs/super.c =================================================================== --- linux-2.6.orig/fs/super.c +++ linux-2.6/fs/super.c @@ -80,6 +80,8 @@ static struct super_block *alloc_super(v sema_init(&s->s_dquot.dqio_sem, 1); sema_init(&s->s_dquot.dqonoff_sem, 1); init_rwsem(&s->s_dquot.dqptr_sem); + s->s_prunes = 0; + init_waitqueue_head(&s->s_wait_prunes); init_waitqueue_head(&s->s_wait_unfrozen); s->s_maxbytes = MAX_NON_LFS; s->dq_op = sb_dquot_ops; @@ -230,8 +232,8 @@ void generic_shutdown_super(struct super if (root) { sb->s_root = NULL; - shrink_dcache_parent(root); shrink_dcache_anon(&sb->s_anon); + shrink_dcache_parent(root); dput(root); fsync_super(sb); lock_super(sb); Index: linux-2.6/include/linux/fs.h =================================================================== --- linux-2.6.orig/include/linux/fs.h +++ linux-2.6/include/linux/fs.h @@ -833,6 +833,9 @@ struct super_block { struct list_head s_instances; struct quota_info s_dquot; /* Diskquota specific options */ + int s_prunes; + wait_queue_head_t s_wait_prunes; + int s_frozen; wait_queue_head_t s_wait_unfrozen; | |