From ba6d2377c85c9b8a793f455d8c9b6cf31985d70f Mon Sep 17 00:00:00 2001
From: Anton Altaparmakov <aia21@cantab.net>
Date: Sun, 26 Jun 2005 22:12:02 +0100
Subject: NTFS: 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.
Signed-off-by: Anton Altaparmakov <aia21@cantab.net>
---
Documentation/filesystems/ntfs.txt | 5 ++++-
fs/ntfs/ChangeLog | 42 ++++++++++++++++++++++++++++++++++++++
fs/ntfs/mft.c | 29 +++++++++++++++++---------
3 files changed, 65 insertions(+), 11 deletions(-)
diff --git a/Documentation/filesystems/ntfs.txt b/Documentation/filesystems/ntfs.txt
index 1415b96ed4..eef4aca0c7 100644
--- a/Documentation/filesystems/ntfs.txt
+++ b/Documentation/filesystems/ntfs.txt
@@ -451,9 +451,12 @@ Note, a technical ChangeLog aimed at kernel hackers is in fs/ntfs/ChangeLog.
- Implement extension of resident files using the normal file write
code paths, i.e. most very small files can be extended to be a little
bit bigger but not by much.
+ - Add new mount option "disable_sparse". (See list of mount options
+ above for details.)
- Improve handling of ntfs volumes with errors and strange boot sectors
in particular.
- - Fix various bugs.
+ - Fix various bugs including a nasty deadlock that appeared in recent
+ kernels (around 2.6.11-2.6.12 timeframe).
2.1.22:
- Improve handling of ntfs volumes with errors.
- Fix various bugs and race conditions.
diff --git a/fs/ntfs/ChangeLog b/fs/ntfs/ChangeLog
index 3d2cac4061..9709fac653 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 3d0ba8e60a..ac9ff39aa8 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
--
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