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[PATCH] xfs: I/O completion handlers must use NOFS allocations

To: xfs@xxxxxxxxxxx
Subject: [PATCH] xfs: I/O completion handlers must use NOFS allocations
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Mon, 19 Oct 2009 00:00:03 -0400
Cc: Thomas Neumann <tneumann@xxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.19 (2009-01-05)
When complention I/O requests we must not allow the memory allocator to
recurse into the filesystem, as we might deadlock on waiting for the
I/O completion otherwise.  The only thing currently allocting normal
GFP_KERNEL memory is the allocation of the transaction structure for the
unwritten extent conversion.  Add a memflags argument to _xfs_trans_alloc
to allow controlling the allocator behaviour.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reported-by: Thomas Neumann <tneumann@xxxxxxxxxxxxxxxxxxxxx>
Tested-by: Thomas Neumann <tneumann@xxxxxxxxxxxxxxxxxxxxx>

Index: linux-2.6/fs/xfs/xfs_fsops.c
===================================================================
--- linux-2.6.orig/fs/xfs/xfs_fsops.c   2009-10-16 23:08:25.170027882 +0200
+++ linux-2.6/fs/xfs/xfs_fsops.c        2009-10-16 23:09:22.904256700 +0200
@@ -611,7 +611,7 @@ xfs_fs_log_dummy(
        xfs_inode_t     *ip;
        int             error;
 
-       tp = _xfs_trans_alloc(mp, XFS_TRANS_DUMMY1);
+       tp = _xfs_trans_alloc(mp, XFS_TRANS_DUMMY1, KM_SLEEP);
        error = xfs_trans_reserve(tp, 0, XFS_ICHANGE_LOG_RES(mp), 0, 0, 0);
        if (error) {
                xfs_trans_cancel(tp, 0);
Index: linux-2.6/fs/xfs/xfs_iomap.c
===================================================================
--- linux-2.6.orig/fs/xfs/xfs_iomap.c   2009-10-16 23:10:14.342278346 +0200
+++ linux-2.6/fs/xfs/xfs_iomap.c        2009-10-16 23:12:08.148004392 +0200
@@ -860,8 +860,15 @@ xfs_iomap_write_unwritten(
                 * set up a transaction to convert the range of extents
                 * from unwritten to real. Do allocations in a loop until
                 * we have covered the range passed in.
+                *
+                * Note that we opencoding the transaction allocation here
+                * to pass KM_NOFS - we can't risk to recurse back into
+                * the filesystem here as we might be asked to write out
+                * the same inode that we complete here and might deadlock
+                * on the iolock.
                 */
-               tp = xfs_trans_alloc(mp, XFS_TRANS_STRAT_WRITE);
+               xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
+               tp = _xfs_trans_alloc(mp, XFS_TRANS_STRAT_WRITE, KM_NOFS);
                tp->t_flags |= XFS_TRANS_RESERVE;
                error = xfs_trans_reserve(tp, resblks,
                                XFS_WRITE_LOG_RES(mp), 0,
Index: linux-2.6/fs/xfs/xfs_mount.c
===================================================================
--- linux-2.6.orig/fs/xfs/xfs_mount.c   2009-10-16 23:08:25.147024815 +0200
+++ linux-2.6/fs/xfs/xfs_mount.c        2009-10-16 23:09:25.127005437 +0200
@@ -1471,7 +1471,7 @@ xfs_log_sbcount(
        if (!xfs_sb_version_haslazysbcount(&mp->m_sb))
                return 0;
 
-       tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT);
+       tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT, KM_SLEEP);
        error = xfs_trans_reserve(tp, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
                                        XFS_DEFAULT_LOG_COUNT);
        if (error) {
Index: linux-2.6/fs/xfs/xfs_trans.c
===================================================================
--- linux-2.6.orig/fs/xfs/xfs_trans.c   2009-10-16 23:08:25.117003816 +0200
+++ linux-2.6/fs/xfs/xfs_trans.c        2009-10-16 23:08:58.202005942 +0200
@@ -236,19 +236,20 @@ xfs_trans_alloc(
        uint            type)
 {
        xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
-       return _xfs_trans_alloc(mp, type);
+       return _xfs_trans_alloc(mp, type, KM_SLEEP);
 }
 
 xfs_trans_t *
 _xfs_trans_alloc(
        xfs_mount_t     *mp,
-       uint            type)
+       uint            type,
+       uint            memflags)
 {
        xfs_trans_t     *tp;
 
        atomic_inc(&mp->m_active_trans);
 
-       tp = kmem_zone_zalloc(xfs_trans_zone, KM_SLEEP);
+       tp = kmem_zone_zalloc(xfs_trans_zone, memflags);
        tp->t_magic = XFS_TRANS_MAGIC;
        tp->t_type = type;
        tp->t_mountp = mp;
Index: linux-2.6/fs/xfs/xfs_trans.h
===================================================================
--- linux-2.6.orig/fs/xfs/xfs_trans.h   2009-10-16 23:08:25.127003692 +0200
+++ linux-2.6/fs/xfs/xfs_trans.h        2009-10-16 23:09:04.726256000 +0200
@@ -924,7 +924,7 @@ typedef struct xfs_trans {
  * XFS transaction mechanism exported interfaces.
  */
 xfs_trans_t    *xfs_trans_alloc(struct xfs_mount *, uint);
-xfs_trans_t    *_xfs_trans_alloc(struct xfs_mount *, uint);
+xfs_trans_t    *_xfs_trans_alloc(struct xfs_mount *, uint, uint);
 xfs_trans_t    *xfs_trans_dup(xfs_trans_t *);
 int            xfs_trans_reserve(xfs_trans_t *, uint, uint, uint,
                                  uint, uint);

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