xfs: introduce mmap/truncate lock

Right now we cannot serialise mmap against truncate or hole punch
sanely. ->page_mkwrite is not able to take locks that the read IO
path normally takes (i.e. the inode iolock) because that could
result in lock inversions (read - iolock - page fault - page_mkwrite
- iolock) and so we cannot use an IO path lock to serialise page
write faults against truncate operations.

Instead, introduce a new lock that is used *only* in the
->page_mkwrite path that is the equivalent of the iolock. The lock
ordering in a page fault is i_mmaplock -> page lock -> i_ilock,
and so in truncate we can i_iolock -> i_mmaplock and so lock out
new write faults during the process of truncation.

Because i_mmap_lock is outside the page lock, we can hold it across
all the same operations we hold the i_iolock for. The only
difference is that we never hold the i_mmaplock in the normal IO
path and so do not ever have the possibility that we can page fault
inside it. Hence there are no recursion issues on the i_mmap_lock
and so we can use it to serialise page fault IO against inode
modification operations that affect the IO path.

This patch introduces the i_mmaplock infrastructure, lockdep
annotations and initialisation/destruction code. Use of the new lock
will be in subsequent patches.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 22 insertions, 7 deletions

diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 86cd6b39bed7..f65ab8176c2f 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -56,6 +56,7 @@ typedef struct xfs_inode {
         struct xfs_inode_log_item *i_itemp;     /* logging information */
         mrlock_t                i_lock;         /* inode lock */
         mrlock_t                i_iolock;       /* inode IO lock */
+        mrlock_t                i_mmaplock;     /* inode mmap IO lock */
         atomic_t                i_pincount;     /* inode pin count */
         spinlock_t              i_flags_lock;   /* inode i_flags lock */
         /* Miscellaneous state. */
@@ -263,15 +264,20 @@ static inline int xfs_isiflocked(struct xfs_inode *ip)
 #define XFS_IOLOCK_SHARED       (1<<1)
 #define XFS_ILOCK_EXCL          (1<<2)
 #define XFS_ILOCK_SHARED        (1<<3)
+#define XFS_MMAPLOCK_EXCL       (1<<4)
+#define XFS_MMAPLOCK_SHARED     (1<<5)
 
 #define XFS_LOCK_MASK           (XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED \
-                                | XFS_ILOCK_EXCL | XFS_ILOCK_SHARED)
+                                | XFS_ILOCK_EXCL | XFS_ILOCK_SHARED \
+                                | XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED)
 
 #define XFS_LOCK_FLAGS \
         { XFS_IOLOCK_EXCL,      "IOLOCK_EXCL" }, \
         { XFS_IOLOCK_SHARED,    "IOLOCK_SHARED" }, \
         { XFS_ILOCK_EXCL,       "ILOCK_EXCL" }, \
-        { XFS_ILOCK_SHARED,     "ILOCK_SHARED" }
+        { XFS_ILOCK_SHARED,     "ILOCK_SHARED" }, \
+        { XFS_MMAPLOCK_EXCL,    "MMAPLOCK_EXCL" }, \
+        { XFS_MMAPLOCK_SHARED,  "MMAPLOCK_SHARED" }
 
 
 /*
@@ -302,17 +308,26 @@ static inline int xfs_isiflocked(struct xfs_inode *ip)
 #define XFS_IOLOCK_SHIFT        16
 #define XFS_IOLOCK_PARENT       (XFS_LOCK_PARENT << XFS_IOLOCK_SHIFT)
 
+#define XFS_MMAPLOCK_SHIFT      20
+
 #define XFS_ILOCK_SHIFT         24
 #define XFS_ILOCK_PARENT        (XFS_LOCK_PARENT << XFS_ILOCK_SHIFT)
 #define XFS_ILOCK_RTBITMAP      (XFS_LOCK_RTBITMAP << XFS_ILOCK_SHIFT)
 #define XFS_ILOCK_RTSUM         (XFS_LOCK_RTSUM << XFS_ILOCK_SHIFT)
 
-#define XFS_IOLOCK_DEP_MASK     0x00ff0000
+#define XFS_IOLOCK_DEP_MASK     0x000f0000
+#define XFS_MMAPLOCK_DEP_MASK   0x00f00000
 #define XFS_ILOCK_DEP_MASK      0xff000000
-#define XFS_LOCK_DEP_MASK       (XFS_IOLOCK_DEP_MASK | XFS_ILOCK_DEP_MASK)
-
-#define XFS_IOLOCK_DEP(flags)   (((flags) & XFS_IOLOCK_DEP_MASK) >> XFS_IOLOCK_SHIFT)
-#define XFS_ILOCK_DEP(flags)    (((flags) & XFS_ILOCK_DEP_MASK) >> XFS_ILOCK_SHIFT)
+#define XFS_LOCK_DEP_MASK       (XFS_IOLOCK_DEP_MASK | \
+                                 XFS_MMAPLOCK_DEP_MASK | \
+                                 XFS_ILOCK_DEP_MASK)
+
+#define XFS_IOLOCK_DEP(flags)   (((flags) & XFS_IOLOCK_DEP_MASK) \
+                                        >> XFS_IOLOCK_SHIFT)
+#define XFS_MMAPLOCK_DEP(flags) (((flags) & XFS_MMAPLOCK_DEP_MASK) \
+                                        >> XFS_MMAPLOCK_SHIFT)
+#define XFS_ILOCK_DEP(flags)    (((flags) & XFS_ILOCK_DEP_MASK) \
+                                        >> XFS_ILOCK_SHIFT)
 
 /*
  * For multiple groups support: if S_ISGID bit is set in the parent