2 files changed, 61 insertions, 10 deletions

diff --git a/fs/ntfs/ChangeLog b/fs/ntfs/ChangeLog
index 3d2cac4061d6..9709fac6531d 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.
 
diff --git a/fs/ntfs/mft.c b/fs/ntfs/mft.c
index 3d0ba8e60adc..ac9ff39aa834 100644
--- a/fs/ntfs/mft.c
+++ b/fs/ntfs/mft.c
@@ -948,20 +948,23 @@ BOOL ntfs_may_write_mft_record(ntfs_volume *vol, const unsigned long mft_no,
         na.name_len = 0;
         na.type = AT_UNUSED;
         /*
-         * For inode 0, i.e. $MFT itself, we cannot use ilookup5() from here or
-         * we deadlock because the inode is already locked by the kernel
-         * (fs/fs-writeback.c::__sync_single_inode()) and ilookup5() waits
-         * until the inode is unlocked before returning it and it never gets
-         * unlocked because ntfs_should_write_mft_record() never returns.  )-:
-         * Fortunately, we have inode 0 pinned in icache for the duration of
-         * the mount so we can access it directly.
+         * Optimize inode 0, i.e. $MFT itself, since we have it in memory and
+         * we get here for it rather often.
          */
         if (!mft_no) {
                 /* Balance the below iput(). */
                 vi = igrab(mft_vi);
                 BUG_ON(vi != mft_vi);
-        } else
-                vi = ilookup5(sb, mft_no, (test_t)ntfs_test_inode, &na);
+        } else {
+                /*
+                 * Have to use ilookup5_nowait() since ilookup5() waits for the
+                 * inode lock which causes ntfs to deadlock when a concurrent
+                 * inode write via the inode dirty code paths and the page
+                 * dirty code path of the inode dirty code path when writing
+                 * $MFT occurs.
+                 */
+                vi = ilookup5_nowait(sb, mft_no, (test_t)ntfs_test_inode, &na);
+        }
         if (vi) {
                 ntfs_debug("Base inode 0x%lx is in icache.", mft_no);
                 /* The inode is in icache. */
@@ -1016,7 +1019,13 @@ BOOL ntfs_may_write_mft_record(ntfs_volume *vol, const unsigned long mft_no,
         na.mft_no = MREF_LE(m->base_mft_record);
         ntfs_debug("Mft record 0x%lx is an extent record.  Looking for base "
                         "inode 0x%lx in icache.", mft_no, na.mft_no);
-        vi = ilookup5(sb, na.mft_no, (test_t)ntfs_test_inode, &na);
+        if (!na.mft_no) {
+                /* Balance the below iput(). */
+                vi = igrab(mft_vi);
+                BUG_ON(vi != mft_vi);
+        } else
+                vi = ilookup5_nowait(sb, na.mft_no, (test_t)ntfs_test_inode,
+                                &na);
         if (!vi) {
                 /*
                  * The base inode is not in icache, write this extent mft