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ext4: avoid deadlock on sync-mounted FS w/o journal
Processes hang forever on a sync-mounted ext2 file system that is mounted with the ext4 module (default in Fedora 16). I can reproduce this reliably by mounting an ext2 partition with "-o sync" and opening a new file an that partition with vim. vim will hang in "D" state forever. The same happens on ext4 without a journal. I am attaching a small patch here that solves this issue for me. In the sync mounted case without a journal, ext4_handle_dirty_metadata() may call sync_dirty_buffer(), which can't be called with buffer lock held. Also move mb_cache_entry_release inside lock to avoid race fixed previously by8a2bfdcb
ext[34]: EA block reference count racing fix Note too that ext2 fixed this same problem in 2006 withb2f49033
[PATCH] fix deadlock in ext2 Signed-off-by: Martin.Wilck@ts.fujitsu.com [sandeen@redhat.com: move mb_cache_entry_release before unlock, edit commit msg] Signed-off-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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@ -484,18 +484,19 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
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ext4_free_blocks(handle, inode, bh, 0, 1,
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EXT4_FREE_BLOCKS_METADATA |
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EXT4_FREE_BLOCKS_FORGET);
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unlock_buffer(bh);
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} else {
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le32_add_cpu(&BHDR(bh)->h_refcount, -1);
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if (ce)
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mb_cache_entry_release(ce);
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unlock_buffer(bh);
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error = ext4_handle_dirty_metadata(handle, inode, bh);
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if (IS_SYNC(inode))
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ext4_handle_sync(handle);
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dquot_free_block(inode, 1);
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ea_bdebug(bh, "refcount now=%d; releasing",
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le32_to_cpu(BHDR(bh)->h_refcount));
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if (ce)
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mb_cache_entry_release(ce);
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}
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unlock_buffer(bh);
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out:
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ext4_std_error(inode->i_sb, error);
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return;
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