xfs: introduce XFS_BMAPI_STACK_SWITCH

Certain allocation paths through xfs_bmapi_write() are in situations
where we have limited stack available. These are almost always in
the buffered IO writeback path when convertion delayed allocation
extents to real extents.

The current stack switch occurs for userdata allocations, which
means we also do stack switches for preallocation, direct IO and
unwritten extent conversion, even those these call chains have never
been implicated in a stack overrun.

Hence, let's target just the single stack overun offended for stack
switches. To do that, introduce a XFS_BMAPI_STACK_SWITCH flag that
the caller can pass xfs_bmapi_write() to indicate it should switch
stacks if it needs to do allocation.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/fs/xfs/xfs_bmap.h b/fs/xfs/xfs_bmap.h
index 803b56d7ce16..b68c598034c1 100644
--- a/fs/xfs/xfs_bmap.h
+++ b/fs/xfs/xfs_bmap.h
@@ -77,6 +77,7 @@ typedef	struct xfs_bmap_free
  * from written to unwritten, otherwise convert from unwritten to written.
  */
 #define XFS_BMAPI_CONVERT       0x040
+#define XFS_BMAPI_STACK_SWITCH  0x080
 
 #define XFS_BMAPI_FLAGS \
         { XFS_BMAPI_ENTIRE,     "ENTIRE" }, \
@@ -85,7 +86,8 @@ typedef	struct xfs_bmap_free
         { XFS_BMAPI_PREALLOC,   "PREALLOC" }, \
         { XFS_BMAPI_IGSTATE,    "IGSTATE" }, \
         { XFS_BMAPI_CONTIG,     "CONTIG" }, \
-        { XFS_BMAPI_CONVERT,    "CONVERT" }
+        { XFS_BMAPI_CONVERT,    "CONVERT" }, \
+        { XFS_BMAPI_STACK_SWITCH, "STACK_SWITCH" }
 
 
 static inline int xfs_bmapi_aflag(int w)
@@ -133,6 +135,7 @@ typedef struct xfs_bmalloca {
         char                    userdata;/* set if is user data */
         char                    aeof;   /* allocated space at eof */
         char                    conv;   /* overwriting unwritten extents */
+        char                    stack_switch;
 } xfs_bmalloca_t;
 
 /*