Btrfs: fix lockdep warning on deadlock against an inode's log mutex

Commit 44f714dae50a ("Btrfs: improve performance on fsync against new
inode after rename/unlink"), which landed in 4.8-rc2, introduced a
possibility for a deadlock due to double locking of an inode's log mutex
by the same task, which lockdep reports with:

[23045.433975] =============================================
[23045.434748] [ INFO: possible recursive locking detected ]
[23045.435426] 4.7.0-rc6-btrfs-next-34+ #1 Not tainted
[23045.436044] ---------------------------------------------
[23045.436044] xfs_io/3688 is trying to acquire lock:
[23045.436044]  (&ei->log_mutex){+.+...}, at: [<ffffffffa038552d>] btrfs_log_inode+0x13a/0xc95 [btrfs]
[23045.436044]
               but task is already holding lock:
[23045.436044]  (&ei->log_mutex){+.+...}, at: [<ffffffffa038552d>] btrfs_log_inode+0x13a/0xc95 [btrfs]
[23045.436044]
               other info that might help us debug this:
[23045.436044]  Possible unsafe locking scenario:

[23045.436044]        CPU0
[23045.436044]        ----
[23045.436044]   lock(&ei->log_mutex);
[23045.436044]   lock(&ei->log_mutex);
[23045.436044]
                *** DEADLOCK ***

[23045.436044]  May be due to missing lock nesting notation

[23045.436044] 3 locks held by xfs_io/3688:
[23045.436044]  #0:  (&sb->s_type->i_mutex_key#15){+.+...}, at: [<ffffffffa035f2ae>] btrfs_sync_file+0x14e/0x425 [btrfs]
[23045.436044]  #1:  (sb_internal#2){.+.+.+}, at: [<ffffffff8118446b>] __sb_start_write+0x5f/0xb0
[23045.436044]  #2:  (&ei->log_mutex){+.+...}, at: [<ffffffffa038552d>] btrfs_log_inode+0x13a/0xc95 [btrfs]
[23045.436044]
               stack backtrace:
[23045.436044] CPU: 4 PID: 3688 Comm: xfs_io Not tainted 4.7.0-rc6-btrfs-next-34+ #1
[23045.436044] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
[23045.436044]  0000000000000000 ffff88022f5f7860 ffffffff8127074d ffffffff82a54b70
[23045.436044]  ffffffff82a54b70 ffff88022f5f7920 ffffffff81092897 ffff880228015d68
[23045.436044]  0000000000000000 ffffffff82a54b70 ffffffff829c3f00 ffff880228015d68
[23045.436044] Call Trace:
[23045.436044]  [<ffffffff8127074d>] dump_stack+0x67/0x90
[23045.436044]  [<ffffffff81092897>] __lock_acquire+0xcbb/0xe4e
[23045.436044]  [<ffffffff8109155f>] ? mark_lock+0x24/0x201
[23045.436044]  [<ffffffff8109179a>] ? mark_held_locks+0x5e/0x74
[23045.436044]  [<ffffffff81092de0>] lock_acquire+0x12f/0x1c3
[23045.436044]  [<ffffffff81092de0>] ? lock_acquire+0x12f/0x1c3
[23045.436044]  [<ffffffffa038552d>] ? btrfs_log_inode+0x13a/0xc95 [btrfs]
[23045.436044]  [<ffffffffa038552d>] ? btrfs_log_inode+0x13a/0xc95 [btrfs]
[23045.436044]  [<ffffffff814a51a4>] mutex_lock_nested+0x77/0x3a7
[23045.436044]  [<ffffffffa038552d>] ? btrfs_log_inode+0x13a/0xc95 [btrfs]
[23045.436044]  [<ffffffffa039705e>] ? btrfs_release_delayed_node+0xb/0xd [btrfs]
[23045.436044]  [<ffffffffa038552d>] btrfs_log_inode+0x13a/0xc95 [btrfs]
[23045.436044]  [<ffffffffa038552d>] ? btrfs_log_inode+0x13a/0xc95 [btrfs]
[23045.436044]  [<ffffffff810a0ed1>] ? vprintk_emit+0x453/0x465
[23045.436044]  [<ffffffffa0385a61>] btrfs_log_inode+0x66e/0xc95 [btrfs]
[23045.436044]  [<ffffffffa03c084d>] log_new_dir_dentries+0x26c/0x359 [btrfs]
[23045.436044]  [<ffffffffa03865aa>] btrfs_log_inode_parent+0x4a6/0x628 [btrfs]
[23045.436044]  [<ffffffffa0387552>] btrfs_log_dentry_safe+0x5a/0x75 [btrfs]
[23045.436044]  [<ffffffffa035f464>] btrfs_sync_file+0x304/0x425 [btrfs]
[23045.436044]  [<ffffffff811acaf4>] vfs_fsync_range+0x8c/0x9e
[23045.436044]  [<ffffffff811acb22>] vfs_fsync+0x1c/0x1e
[23045.436044]  [<ffffffff811acc79>] do_fsync+0x31/0x4a
[23045.436044]  [<ffffffff811ace99>] SyS_fsync+0x10/0x14
[23045.436044]  [<ffffffff814a88e5>] entry_SYSCALL_64_fastpath+0x18/0xa8
[23045.436044]  [<ffffffff8108f039>] ? trace_hardirqs_off_caller+0x3f/0xaa

An example reproducer for this is:

   $ mkfs.btrfs -f /dev/sdb
   $ mount /dev/sdb /mnt
   $ mkdir /mnt/dir
   $ touch /mnt/dir/foo
   $ sync
   $ mv /mnt/dir/foo /mnt/dir/bar
   $ touch /mnt/dir/foo
   $ xfs_io -c "fsync" /mnt/dir/bar

This is because while logging the inode of file bar we end up logging its
parent directory (since its inode has an unlink_trans field matching the
current transaction id due to the rename operation), which in turn logs
the inodes for all its new dentries, so that the new inode for the new
file named foo gets logged which in turn triggered another logging attempt
for the inode we are fsync'ing, since that inode had an old name that
corresponds to the name of the new inode.

So fix this by ensuring that when logging the inode for a new dentry that
has a name matching an old name of some other inode, we don't log again
the original inode that we are fsync'ing.

Fixes: 44f714dae50a ("Btrfs: improve performance on fsync against new inode after rename/unlink")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 3391f2adf0c869466d47124461e62c2ee3bf3989..fea31a4a6e36844d97a53c80a7f442c166e82b60 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2070,7 +2070,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
        }
        trans->sync = true;
 
-       btrfs_init_log_ctx(&ctx);
+       btrfs_init_log_ctx(&ctx, inode);
 
        ret = btrfs_log_dentry_safe(trans, root, dentry, start, end, &ctx);
        if (ret < 0) {

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index ffe92da81b8ace42dfd6f15f9d261fb62c113d2c..e935035ac03435295c6bfcf9fd58c2b4978e65c8 100644 (file)
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2823,7 +2823,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
         */
        mutex_unlock(&root->log_mutex);
 
-       btrfs_init_log_ctx(&root_log_ctx);
+       btrfs_init_log_ctx(&root_log_ctx, NULL);
 
        mutex_lock(&log_root_tree->log_mutex);
        atomic_inc(&log_root_tree->log_batch);
@@ -4757,7 +4757,8 @@ static int btrfs_log_inode(struct btrfs_trans_handle *trans,
                        if (ret < 0) {
                                err = ret;
                                goto out_unlock;
-                       } else if (ret > 0) {
+                       } else if (ret > 0 && ctx &&
+                                  other_ino != btrfs_ino(ctx->inode)) {
                                struct btrfs_key inode_key;
                                struct inode *other_inode;
 

diff --git a/fs/btrfs/tree-log.h b/fs/btrfs/tree-log.h
index a9f1b75d080d3796756c9e9f09c04180b404eb1c..ab858e31ccbc2210a01a9b7ce69bf52127d00b8b 100644 (file)
--- a/fs/btrfs/tree-log.h
+++ b/fs/btrfs/tree-log.h
@@ -30,15 +30,18 @@ struct btrfs_log_ctx {
        int log_transid;
        int io_err;
        bool log_new_dentries;
+       struct inode *inode;
        struct list_head list;
 };
 
-static inline void btrfs_init_log_ctx(struct btrfs_log_ctx *ctx)
+static inline void btrfs_init_log_ctx(struct btrfs_log_ctx *ctx,
+                                     struct inode *inode)
 {
        ctx->log_ret = 0;
        ctx->log_transid = 0;
        ctx->io_err = 0;
        ctx->log_new_dentries = false;
+       ctx->inode = inode;
        INIT_LIST_HEAD(&ctx->list);
 }