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authorDave Chinner <dchinner@redhat.com>2012-11-28 13:01:00 +1100
committerBen Myers <bpm@sgi.com>2012-11-29 14:22:56 -0600
commit437a255aa23766666aec78af63be4c253faa8d57 (patch)
treefe35390067b0b0f3efc47420c454d6d6de7892c6 /fs/xfs
parentef9d873344ff9f5084eacb9f3735982314dfda9e (diff)
xfs: fix direct IO nested transaction deadlock.
The direct IO path can do a nested transaction reservation when writing past the EOF. The first transaction is the append transaction for setting the filesize at IO completion, but we can also need a transaction for allocation of blocks. If the log is low on space due to reservations and small log, the append transaction can be granted after wating for space as the only active transaction in the system. This then attempts a reservation for an allocation, which there isn't space in the log for, and the reservation sleeps. The result is that there is nothing left in the system to wake up all the processes waiting for log space to come free. The stack trace that shows this deadlock is relatively innocuous: xlog_grant_head_wait xlog_grant_head_check xfs_log_reserve xfs_trans_reserve xfs_iomap_write_direct __xfs_get_blocks xfs_get_blocks_direct do_blockdev_direct_IO __blockdev_direct_IO xfs_vm_direct_IO generic_file_direct_write xfs_file_dio_aio_writ xfs_file_aio_write do_sync_write vfs_write This was discovered on a filesystem with a log of only 10MB, and a log stripe unit of 256k whih increased the base reservations by 512k. Hence a allocation transaction requires 1.2MB of log space to be available instead of only 260k, and so greatly increased the chance that there wouldn't be enough log space available for the nested transaction to succeed. The key to reproducing it is this mkfs command: mkfs.xfs -f -d agcount=16,su=256k,sw=12 -l su=256k,size=2560b $SCRATCH_DEV The test case was a 1000 fsstress processes running with random freeze and unfreezes every few seconds. Thanks to Eryu Guan (eguan@redhat.com) for writing the test that found this on a system with a somewhat unique default configuration.... cc: <stable@vger.kernel.org> Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Andrew Dahl <adahl@sgi.com> Signed-off-by: Ben Myers <bpm@sgi.com>
Diffstat (limited to 'fs/xfs')
-rw-r--r--fs/xfs/xfs_aops.c81
-rw-r--r--fs/xfs/xfs_log.c3
2 files changed, 31 insertions, 53 deletions
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 71361da1f77..4111a40ebe1 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -124,7 +124,7 @@ xfs_setfilesize_trans_alloc(
ioend->io_append_trans = tp;
/*
- * We will pass freeze protection with a transaction. So tell lockdep
+ * We may pass freeze protection with a transaction. So tell lockdep
* we released it.
*/
rwsem_release(&ioend->io_inode->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
@@ -149,11 +149,13 @@ xfs_setfilesize(
xfs_fsize_t isize;
/*
- * The transaction was allocated in the I/O submission thread,
- * thus we need to mark ourselves as beeing in a transaction
- * manually.
+ * The transaction may have been allocated in the I/O submission thread,
+ * thus we need to mark ourselves as beeing in a transaction manually.
+ * Similarly for freeze protection.
*/
current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);
+ rwsem_acquire_read(&VFS_I(ip)->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
+ 0, 1, _THIS_IP_);
xfs_ilock(ip, XFS_ILOCK_EXCL);
isize = xfs_new_eof(ip, ioend->io_offset + ioend->io_size);
@@ -187,7 +189,8 @@ xfs_finish_ioend(
if (ioend->io_type == XFS_IO_UNWRITTEN)
queue_work(mp->m_unwritten_workqueue, &ioend->io_work);
- else if (ioend->io_append_trans)
+ else if (ioend->io_append_trans ||
+ (ioend->io_isdirect && xfs_ioend_is_append(ioend)))
queue_work(mp->m_data_workqueue, &ioend->io_work);
else
xfs_destroy_ioend(ioend);
@@ -205,15 +208,6 @@ xfs_end_io(
struct xfs_inode *ip = XFS_I(ioend->io_inode);
int error = 0;
- if (ioend->io_append_trans) {
- /*
- * We've got freeze protection passed with the transaction.
- * Tell lockdep about it.
- */
- rwsem_acquire_read(
- &ioend->io_inode->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
- 0, 1, _THIS_IP_);
- }
if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
ioend->io_error = -EIO;
goto done;
@@ -226,35 +220,31 @@ xfs_end_io(
* range to normal written extens after the data I/O has finished.
*/
if (ioend->io_type == XFS_IO_UNWRITTEN) {
+ error = xfs_iomap_write_unwritten(ip, ioend->io_offset,
+ ioend->io_size);
+ } else if (ioend->io_isdirect && xfs_ioend_is_append(ioend)) {
/*
- * For buffered I/O we never preallocate a transaction when
- * doing the unwritten extent conversion, but for direct I/O
- * we do not know if we are converting an unwritten extent
- * or not at the point where we preallocate the transaction.
+ * For direct I/O we do not know if we need to allocate blocks
+ * or not so we can't preallocate an append transaction as that
+ * results in nested reservations and log space deadlocks. Hence
+ * allocate the transaction here. While this is sub-optimal and
+ * can block IO completion for some time, we're stuck with doing
+ * it this way until we can pass the ioend to the direct IO
+ * allocation callbacks and avoid nesting that way.
*/
- if (ioend->io_append_trans) {
- ASSERT(ioend->io_isdirect);
-
- current_set_flags_nested(
- &ioend->io_append_trans->t_pflags, PF_FSTRANS);
- xfs_trans_cancel(ioend->io_append_trans, 0);
- }
-
- error = xfs_iomap_write_unwritten(ip, ioend->io_offset,
- ioend->io_size);
- if (error) {
- ioend->io_error = -error;
+ error = xfs_setfilesize_trans_alloc(ioend);
+ if (error)
goto done;
- }
+ error = xfs_setfilesize(ioend);
} else if (ioend->io_append_trans) {
error = xfs_setfilesize(ioend);
- if (error)
- ioend->io_error = -error;
} else {
ASSERT(!xfs_ioend_is_append(ioend));
}
done:
+ if (error)
+ ioend->io_error = -error;
xfs_destroy_ioend(ioend);
}
@@ -1432,25 +1422,21 @@ xfs_vm_direct_IO(
size_t size = iov_length(iov, nr_segs);
/*
- * We need to preallocate a transaction for a size update
- * here. In the case that this write both updates the size
- * and converts at least on unwritten extent we will cancel
- * the still clean transaction after the I/O has finished.
+ * We cannot preallocate a size update transaction here as we
+ * don't know whether allocation is necessary or not. Hence we
+ * can only tell IO completion that one is necessary if we are
+ * not doing unwritten extent conversion.
*/
iocb->private = ioend = xfs_alloc_ioend(inode, XFS_IO_DIRECT);
- if (offset + size > XFS_I(inode)->i_d.di_size) {
- ret = xfs_setfilesize_trans_alloc(ioend);
- if (ret)
- goto out_destroy_ioend;
+ if (offset + size > XFS_I(inode)->i_d.di_size)
ioend->io_isdirect = 1;
- }
ret = __blockdev_direct_IO(rw, iocb, inode, bdev, iov,
offset, nr_segs,
xfs_get_blocks_direct,
xfs_end_io_direct_write, NULL, 0);
if (ret != -EIOCBQUEUED && iocb->private)
- goto out_trans_cancel;
+ goto out_destroy_ioend;
} else {
ret = __blockdev_direct_IO(rw, iocb, inode, bdev, iov,
offset, nr_segs,
@@ -1460,15 +1446,6 @@ xfs_vm_direct_IO(
return ret;
-out_trans_cancel:
- if (ioend->io_append_trans) {
- current_set_flags_nested(&ioend->io_append_trans->t_pflags,
- PF_FSTRANS);
- rwsem_acquire_read(
- &inode->i_sb->s_writers.lock_map[SB_FREEZE_FS-1],
- 0, 1, _THIS_IP_);
- xfs_trans_cancel(ioend->io_append_trans, 0);
- }
out_destroy_ioend:
xfs_destroy_ioend(ioend);
return ret;
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index c6d6e136ba7..c49e2c12dba 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -460,7 +460,8 @@ xfs_log_reserve(
tic->t_trans_type = t_type;
*ticp = tic;
- xlog_grant_push_ail(log, tic->t_unit_res * tic->t_cnt);
+ xlog_grant_push_ail(log, tic->t_cnt ? tic->t_unit_res * tic->t_cnt
+ : tic->t_unit_res);
trace_xfs_log_reserve(log, tic);