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Btrfs: fix btrfs_write_inode vs delayed iput deadlock
We recently ran into the following deadlock involving btrfs_write_inode(): [ +0.005066] __schedule+0x38e/0x8c0 [ +0.007144] schedule+0x36/0x80 [ +0.006447] bit_wait+0x11/0x60 [ +0.006446] __wait_on_bit+0xbe/0x110 [ +0.007487] ? bit_wait_io+0x60/0x60 [ +0.007319] __inode_wait_for_writeback+0x96/0xc0 [ +0.009568] ? autoremove_wake_function+0x40/0x40 [ +0.009565] inode_wait_for_writeback+0x21/0x30 [ +0.009224] evict+0xb0/0x190 [ +0.006099] iput+0x1a8/0x210 [ +0.006103] btrfs_run_delayed_iputs+0x73/0xc0 [ +0.009047] btrfs_commit_transaction+0x799/0x8c0 [ +0.009567] btrfs_write_inode+0x81/0xb0 [ +0.008008] __writeback_single_inode+0x267/0x320 [ +0.009569] writeback_sb_inodes+0x25b/0x4e0 [ +0.008702] wb_writeback+0x102/0x2d0 [ +0.007487] wb_workfn+0xa4/0x310 [ +0.006794] ? wb_workfn+0xa4/0x310 [ +0.007143] process_one_work+0x150/0x410 [ +0.008179] worker_thread+0x6d/0x520 [ +0.007490] kthread+0x12c/0x160 [ +0.006620] ? put_pwq_unlocked+0x80/0x80 [ +0.008185] ? kthread_park+0xa0/0xa0 [ +0.007484] ? do_syscall_64+0x53/0x150 [ +0.007837] ret_from_fork+0x29/0x40 Writeback calls: btrfs_write_inode btrfs_commit_transaction btrfs_run_delayed_iputs If iput() is called on that same inode, evict() will wait for writeback forever. btrfs_write_inode() was originally added way back in4730a4bc5b
("btrfs_dirty_inode") to support O_SYNC writes. However, ->write_inode() hasn't been used for O_SYNC since148f948ba8
("vfs: Introduce new helpers for syncing after writing to O_SYNC file or IS_SYNC inode"), so btrfs_write_inode() is actually unnecessary (and leads to a bunch of unnecessary commits). Get rid of it, which also gets rid of the deadlock. CC: stable@vger.kernel.org # 3.2+ Signed-off-by: Josef Bacik <jbacik@fb.com> [Omar: new commit message] Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: David Sterba <dsterba@suse.com>
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2 changed files with 0 additions and 27 deletions
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@ -6021,32 +6021,6 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
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return ret;
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}
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int btrfs_write_inode(struct inode *inode, struct writeback_control *wbc)
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{
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struct btrfs_root *root = BTRFS_I(inode)->root;
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struct btrfs_trans_handle *trans;
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int ret = 0;
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bool nolock = false;
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if (test_bit(BTRFS_INODE_DUMMY, &BTRFS_I(inode)->runtime_flags))
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return 0;
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if (btrfs_fs_closing(root->fs_info) &&
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btrfs_is_free_space_inode(BTRFS_I(inode)))
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nolock = true;
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if (wbc->sync_mode == WB_SYNC_ALL) {
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if (nolock)
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trans = btrfs_join_transaction_nolock(root);
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else
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trans = btrfs_join_transaction(root);
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if (IS_ERR(trans))
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return PTR_ERR(trans);
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ret = btrfs_commit_transaction(trans);
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}
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return ret;
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}
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/*
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* This is somewhat expensive, updating the tree every time the
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* inode changes. But, it is most likely to find the inode in cache.
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@ -2344,7 +2344,6 @@ static const struct super_operations btrfs_super_ops = {
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.sync_fs = btrfs_sync_fs,
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.show_options = btrfs_show_options,
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.show_devname = btrfs_show_devname,
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.write_inode = btrfs_write_inode,
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.alloc_inode = btrfs_alloc_inode,
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.destroy_inode = btrfs_destroy_inode,
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.statfs = btrfs_statfs,
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