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authorCarlos Maiolino <cmaiolino@redhat.com>2012-08-10 15:01:51 -0300
committerBen Myers <bpm@sgi.com>2012-08-29 15:01:11 -0500
commit6fb8a90aa3f2319a25f3396b1e9273300f8903b8 (patch)
tree3a74bce9dbe7a6ef8b0c952335c1963a649eefa2 /fs/xfs/xfs_buf.h
parenta672e1be30d5bc848cd0067c55ed29b2015b7c17 (diff)
downloadvexpress-lsk-6fb8a90aa3f2319a25f3396b1e9273300f8903b8.tar.gz
xfs: fix race while discarding buffers [V4]
While xfs_buftarg_shrink() is freeing buffers from the dispose list (filled with buffers from lru list), there is a possibility to have xfs_buf_stale() racing with it, and removing buffers from dispose list before xfs_buftarg_shrink() does it. This happens because xfs_buftarg_shrink() handle the dispose list without locking and the test condition in xfs_buf_stale() checks for the buffer being in *any* list: if (!list_empty(&bp->b_lru)) If the buffer happens to be on dispose list, this causes the buffer counter of lru list (btp->bt_lru_nr) to be decremented twice (once in xfs_buftarg_shrink() and another in xfs_buf_stale()) causing a wrong account usage of the lru list. This may cause xfs_buftarg_shrink() to return a wrong value to the memory shrinker shrink_slab(), and such account error may also cause an underflowed value to be returned; since the counter is lower than the current number of items in the lru list, a decrement may happen when the counter is 0, causing an underflow on the counter. The fix uses a new flag field (and a new buffer flag) to serialize buffer handling during the shrink process. The new flag field has been designed to use btp->bt_lru_lock/unlock instead of xfs_buf_lock/unlock mechanism. dchinner, sandeen, aquini and aris also deserve credits for this. Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com> Reviewed-by: Ben Myers <bpm@sgi.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Ben Myers <bpm@sgi.com>
Diffstat (limited to 'fs/xfs/xfs_buf.h')
-rw-r--r--fs/xfs/xfs_buf.h41
1 files changed, 24 insertions, 17 deletions
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index d03b73b9604..7c0b6a0a155 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -38,27 +38,28 @@ typedef enum {
XBRW_ZERO = 3, /* Zero target memory */
} xfs_buf_rw_t;
-#define XBF_READ (1 << 0) /* buffer intended for reading from device */
-#define XBF_WRITE (1 << 1) /* buffer intended for writing to device */
-#define XBF_READ_AHEAD (1 << 2) /* asynchronous read-ahead */
-#define XBF_ASYNC (1 << 4) /* initiator will not wait for completion */
-#define XBF_DONE (1 << 5) /* all pages in the buffer uptodate */
-#define XBF_STALE (1 << 6) /* buffer has been staled, do not find it */
+#define XBF_READ (1 << 0) /* buffer intended for reading from device */
+#define XBF_WRITE (1 << 1) /* buffer intended for writing to device */
+#define XBF_READ_AHEAD (1 << 2) /* asynchronous read-ahead */
+#define XBF_ASYNC (1 << 4) /* initiator will not wait for completion */
+#define XBF_DONE (1 << 5) /* all pages in the buffer uptodate */
+#define XBF_STALE (1 << 6) /* buffer has been staled, do not find it */
/* I/O hints for the BIO layer */
-#define XBF_SYNCIO (1 << 10)/* treat this buffer as synchronous I/O */
-#define XBF_FUA (1 << 11)/* force cache write through mode */
-#define XBF_FLUSH (1 << 12)/* flush the disk cache before a write */
+#define XBF_SYNCIO (1 << 10)/* treat this buffer as synchronous I/O */
+#define XBF_FUA (1 << 11)/* force cache write through mode */
+#define XBF_FLUSH (1 << 12)/* flush the disk cache before a write */
/* flags used only as arguments to access routines */
-#define XBF_TRYLOCK (1 << 16)/* lock requested, but do not wait */
-#define XBF_UNMAPPED (1 << 17)/* do not map the buffer */
+#define XBF_TRYLOCK (1 << 16)/* lock requested, but do not wait */
+#define XBF_UNMAPPED (1 << 17)/* do not map the buffer */
/* flags used only internally */
-#define _XBF_PAGES (1 << 20)/* backed by refcounted pages */
-#define _XBF_KMEM (1 << 21)/* backed by heap memory */
-#define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */
-#define _XBF_COMPOUND (1 << 23)/* compound buffer */
+#define _XBF_PAGES (1 << 20)/* backed by refcounted pages */
+#define _XBF_KMEM (1 << 21)/* backed by heap memory */
+#define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */
+#define _XBF_COMPOUND (1 << 23)/* compound buffer */
+#define _XBF_LRU_DISPOSE (1 << 24)/* buffer being discarded */
typedef unsigned int xfs_buf_flags_t;
@@ -72,12 +73,13 @@ typedef unsigned int xfs_buf_flags_t;
{ XBF_SYNCIO, "SYNCIO" }, \
{ XBF_FUA, "FUA" }, \
{ XBF_FLUSH, "FLUSH" }, \
- { XBF_TRYLOCK, "TRYLOCK" }, /* should never be set */\
+ { XBF_TRYLOCK, "TRYLOCK" }, /* should never be set */\
{ XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\
{ _XBF_PAGES, "PAGES" }, \
{ _XBF_KMEM, "KMEM" }, \
{ _XBF_DELWRI_Q, "DELWRI_Q" }, \
- { _XBF_COMPOUND, "COMPOUND" }
+ { _XBF_COMPOUND, "COMPOUND" }, \
+ { _XBF_LRU_DISPOSE, "LRU_DISPOSE" }
typedef struct xfs_buftarg {
dev_t bt_dev;
@@ -124,7 +126,12 @@ typedef struct xfs_buf {
xfs_buf_flags_t b_flags; /* status flags */
struct semaphore b_sema; /* semaphore for lockables */
+ /*
+ * concurrent access to b_lru and b_lru_flags are protected by
+ * bt_lru_lock and not by b_sema
+ */
struct list_head b_lru; /* lru list */
+ xfs_buf_flags_t b_lru_flags; /* internal lru status flags */
wait_queue_head_t b_waiters; /* unpin waiters */
struct list_head b_list;
struct xfs_perag *b_pag; /* contains rbtree root */