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88bd5121d6
Something has changed in the core kernel such that we now get concurrent inode write outs, one e.g via pdflush and one via sys_sync or whatever. This causes a nasty deadlock in ntfs. The only clean solution unfortunately requires a minor vfs api extension. First the deadlock analysis: Prerequisive knowledge: NTFS has a file $MFT (inode 0) loaded at mount time. The NTFS driver uses the page cache for storing the file contents as usual. More interestingly this file contains the table of on-disk inodes as a sequence of MFT_RECORDs. Thus NTFS driver accesses the on-disk inodes by accessing the MFT_RECORDs in the page cache pages of the loaded inode $MFT. The situation: VFS inode X on a mounted ntfs volume is dirty. For same inode X, the ntfs_inode is dirty and thus corresponding on-disk inode, which is as explained above in a dirty PAGE_CACHE_PAGE belonging to the table of inodes ($MFT, inode 0). What happens: Process 1: sys_sync()/umount()/whatever... calls __sync_single_inode() for $MFT -> do_writepages() -> write_page for the dirty page containing the on-disk inode X, the page is now locked -> ntfs_write_mst_block() which clears PageUptodate() on the page to prevent anyone else getting hold of it whilst it does the write out (this is necessary as the on-disk inode needs "fixups" applied before the write to disk which are removed again after the write and PageUptodate is then set again). It then analyses the page looking for dirty on-disk inodes and when it finds one it calls ntfs_may_write_mft_record() to see if it is safe to write this on-disk inode. This then calls ilookup5() to check if the corresponding VFS inode is in icache(). This in turn calls ifind() which waits on the inode lock via wait_on_inode whilst holding the global inode_lock. Process 2: pdflush results in a call to __sync_single_inode for the same VFS inode X on the ntfs volume. This locks the inode (I_LOCK) then calls write-inode -> ntfs_write_inode -> map_mft_record() -> read_cache_page() of the page (in page cache of table of inodes $MFT, inode 0) containing the on-disk inode. This page has PageUptodate() clear because of Process 1 (see above) so read_cache_page() blocks when tries to take the page lock for the page so it can call ntfs_read_page(). Thus Process 1 is holding the page lock on the page containing the on-disk inode X and it is waiting on the inode X to be unlocked in ifind() so it can write the page out and then unlock the page. And Process 2 is holding the inode lock on inode X and is waiting for the page to be unlocked so it can call ntfs_readpage() or discover that Process 1 set PageUptodate() again and use the page. Thus we have a deadlock due to ifind() waiting on the inode lock. The only sensible solution: NTFS does not care whether the VFS inode is locked or not when it calls ilookup5() (it doesn't use the VFS inode at all, it just uses it to find the corresponding ntfs_inode which is of course attached to the VFS inode (both are one single struct); and it uses the ntfs_inode which is subject to its own locking so I_LOCK is irrelevant) hence we want a modified ilookup5_nowait() which is the same as ilookup5() but it does not wait on the inode lock. Without such functionality I would have to keep my own ntfs_inode cache in the NTFS driver just so I can find ntfs_inodes independent of their VFS inodes which would be slow, memory and cpu cycle wasting, and incredibly stupid given the icache already exists in the VFS. Below is a patch that does the ilookup5_nowait() implementation in fs/inode.c and exports it. ilookup5_nowait.diff: Introduce ilookup5_nowait() which is basically the same as ilookup5() but it does not wait on the inode's lock (i.e. it omits the wait_on_inode() done in ifind()). This is needed to avoid a nasty deadlock in NTFS. Signed-off-by: Anton Altaparmakov <aia21@cantab.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> |
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| affs | ||
| afs | ||
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| freevxfs | ||
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| hfsplus | ||
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| lockd | ||
| minix | ||
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| nfs | ||
| nfs_common | ||
| nfsd | ||
| nls | ||
| ntfs | ||
| openpromfs | ||
| partitions | ||
| proc | ||
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| smbfs | ||
| sysfs | ||
| sysv | ||
| udf | ||
| ufs | ||
| umsdos | ||
| vfat | ||
| xfs | ||
| aio.c | ||
| attr.c | ||
| bad_inode.c | ||
| binfmt_aout.c | ||
| binfmt_elf_fdpic.c | ||
| binfmt_elf.c | ||
| binfmt_em86.c | ||
| binfmt_flat.c | ||
| binfmt_misc.c | ||
| binfmt_script.c | ||
| binfmt_som.c | ||
| bio.c | ||
| block_dev.c | ||
| buffer.c | ||
| char_dev.c | ||
| compat_ioctl.c | ||
| compat.c | ||
| dcache.c | ||
| dcookies.c | ||
| direct-io.c | ||
| dnotify.c | ||
| dquot.c | ||
| eventpoll.c | ||
| exec.c | ||
| fcntl.c | ||
| fifo.c | ||
| file_table.c | ||
| file.c | ||
| filesystems.c | ||
| fs-writeback.c | ||
| inode.c | ||
| inotify.c | ||
| ioctl.c | ||
| ioprio.c | ||
| Kconfig | ||
| Kconfig.binfmt | ||
| libfs.c | ||
| locks.c | ||
| Makefile | ||
| mbcache.c | ||
| mpage.c | ||
| namei.c | ||
| namespace.c | ||
| nfsctl.c | ||
| open.c | ||
| pipe.c | ||
| posix_acl.c | ||
| quota_v1.c | ||
| quota_v2.c | ||
| quota.c | ||
| read_write.c | ||
| readdir.c | ||
| select.c | ||
| seq_file.c | ||
| stat.c | ||
| super.c | ||
| xattr_acl.c | ||
| xattr.c | ||