xfs: fix mmap_sem/iolock inversion in xfs_free_eofblocks

When xfs_free_eofblocks is called from ->release the VM might already
hold the mmap_sem, but in the write path we take the iolock before
taking the mmap_sem in the generic write code.

Switch xfs_free_eofblocks to only trylock the iolock if called from
->release and skip trimming the prellocated blocks in that case.
We'll still free them later on the final iput.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Alex Elder <aelder@sgi.com>

1 files changed, 26 insertions, 8 deletions

diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
index 3fac146b3b7d..d98401470cf0 100644
--- a/fs/xfs/xfs_vnodeops.c
+++ b/fs/xfs/xfs_vnodeops.c
@@ -709,6 +709,11 @@ xfs_fsync(
 }
 
 /*
+ * Flags for xfs_free_eofblocks
+ */
+#define XFS_FREE_EOF_TRYLOCK    (1<<0)
+
+/*
  * This is called by xfs_inactive to free any blocks beyond eof
  * when the link count isn't zero and by xfs_dm_punch_hole() when
  * punching a hole to EOF.
@@ -726,7 +731,6 @@ xfs_free_eofblocks(
         xfs_filblks_t   map_len;
         int             nimaps;
         xfs_bmbt_irec_t imap;
-        int             use_iolock = (flags & XFS_FREE_EOF_LOCK);
 
         /*
          * Figure out if there are any blocks beyond the end
@@ -768,14 +772,19 @@ xfs_free_eofblocks(
                  * cache and we can't
                  * do that within a transaction.
                  */
-                if (use_iolock)
+                if (flags & XFS_FREE_EOF_TRYLOCK) {
+                        if (!xfs_ilock_nowait(ip, XFS_IOLOCK_EXCL)) {
+                                xfs_trans_cancel(tp, 0);
+                                return 0;
+                        }
+                } else {
                         xfs_ilock(ip, XFS_IOLOCK_EXCL);
+                }
                 error = xfs_itruncate_start(ip, XFS_ITRUNC_DEFINITE,
                                     ip->i_size);
                 if (error) {
                         xfs_trans_cancel(tp, 0);
-                        if (use_iolock)
-                                xfs_iunlock(ip, XFS_IOLOCK_EXCL);
+                        xfs_iunlock(ip, XFS_IOLOCK_EXCL);
                         return error;
                 }
 
@@ -812,8 +821,7 @@ xfs_free_eofblocks(
                         error = xfs_trans_commit(tp,
                                                 XFS_TRANS_RELEASE_LOG_RES);
                 }
-                xfs_iunlock(ip, (use_iolock ? (XFS_IOLOCK_EXCL|XFS_ILOCK_EXCL)
-                                            : XFS_ILOCK_EXCL));
+                xfs_iunlock(ip, XFS_IOLOCK_EXCL|XFS_ILOCK_EXCL);
         }
         return error;
 }
@@ -1113,7 +1121,17 @@ xfs_release(
                      (ip->i_df.if_flags & XFS_IFEXTENTS))  &&
                     (!(ip->i_d.di_flags &
                                 (XFS_DIFLAG_PREALLOC | XFS_DIFLAG_APPEND)))) {
-                        error = xfs_free_eofblocks(mp, ip, XFS_FREE_EOF_LOCK);
+
+                        /*
+                         * If we can't get the iolock just skip truncating
+                         * the blocks past EOF because we could deadlock
+                         * with the mmap_sem otherwise.  We'll get another
+                         * chance to drop them once the last reference to
+                         * the inode is dropped, so we'll never leak blocks
+                         * permanently.
+                         */
+                        error = xfs_free_eofblocks(mp, ip,
+                                                   XFS_FREE_EOF_TRYLOCK);
                         if (error)
                                 return error;
                 }
@@ -1184,7 +1202,7 @@ xfs_inactive(
                      (!(ip->i_d.di_flags &
                                 (XFS_DIFLAG_PREALLOC | XFS_DIFLAG_APPEND)) ||
                       (ip->i_delayed_blks != 0)))) {
-                        error = xfs_free_eofblocks(mp, ip, XFS_FREE_EOF_LOCK);
+                        error = xfs_free_eofblocks(mp, ip, 0);
                         if (error)
                                 return VN_INACTIVE_CACHE;
                 }