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Diffstat (limited to 'fs/ntfs/ChangeLog')
| -rw-r--r-- | fs/ntfs/ChangeLog | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/fs/ntfs/ChangeLog b/fs/ntfs/ChangeLog index 3d2cac4..9709fac 100644 --- a/fs/ntfs/ChangeLog +++ b/fs/ntfs/ChangeLog @@ -132,6 +132,48 @@ ToDo/Notes: the already mapped runlist fragment which causes ntfs_mapping_pairs_decompress() to fail and return error. Update ntfs_attr_find_vcn_nolock() accordingly. + - Fix a nasty deadlock that appeared in recent kernels. + 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, i.e. mft record, which is in a dirty PAGE_CACHE_PAGE belonging + to the table of inodes, i.e. $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() for 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 it 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 solution: The fix is to use the newly introduced + ilookup5_nowait() which does not wait on the inode's lock and hence + avoids the deadlock. This is safe as we do not care about the VFS + inode and only use the fact that it is in the VFS inode cache and the + fact that the vfs and ntfs inodes are one struct in memory to find + the ntfs inode in memory if present. Also, the ntfs inode has its + own locking so it does not matter if the vfs inode is locked. 2.1.22 - Many bug and race fixes and error handling improvements. |
