From c43ad17f7c4e6e68d7d80edc1ed487b3f1d3fe49 Mon Sep 17 00:00:00 2001 From: Brian Foster Date: Tue, 17 Oct 2017 14:16:29 -0700 Subject: [PATCH] xfs: buffer lru reference count error injection tag XFS uses a fixed reference count for certain types of buffers in the internal LRU cache. These reference counts dictate how aggressively certain buffers are reclaimed vs. others. While the reference counts implements priority across different buffer types, all buffers (other than uncached buffers) are typically cached for at least one reclaim cycle. We've had at least one bug recently that has been hidden by a released buffer sitting around in the LRU. Users hitting the problem were able to reproduce under enough memory pressure to cause aggressive reclaim in a particular window of time. To support future xfstests cases, add an error injection tag to hardcode the buffer reference count to zero. When enabled, this bypasses caching of associated buffers and facilitates test cases that depend on this behavior. Signed-off-by: Brian Foster Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong --- fs/xfs/xfs_buf.c | 16 ++++++++++++++++ fs/xfs/xfs_buf.h | 5 +---- fs/xfs/xfs_error.c | 3 +++ fs/xfs/xfs_error.h | 4 +++- 4 files changed, 23 insertions(+), 5 deletions(-) diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 2f97c12ca75e4..d481dd2b29a68 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -42,6 +42,7 @@ #include "xfs_mount.h" #include "xfs_trace.h" #include "xfs_log.h" +#include "xfs_error.h" static kmem_zone_t *xfs_buf_zone; @@ -2129,3 +2130,18 @@ xfs_buf_terminate(void) { kmem_zone_destroy(xfs_buf_zone); } + +void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref) +{ + struct xfs_mount *mp = bp->b_target->bt_mount; + + /* + * Set the lru reference count to 0 based on the error injection tag. + * This allows userspace to disrupt buffer caching for debug/testing + * purposes. + */ + if (XFS_TEST_ERROR(false, mp, XFS_ERRTAG_BUF_LRU_REF)) + lru_ref = 0; + + atomic_set(&bp->b_lru_ref, lru_ref); +} diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h index bf71507ddb165..f873bb7868242 100644 --- a/fs/xfs/xfs_buf.h +++ b/fs/xfs/xfs_buf.h @@ -352,10 +352,7 @@ extern void xfs_buf_terminate(void); #define XFS_BUF_ADDR(bp) ((bp)->b_maps[0].bm_bn) #define XFS_BUF_SET_ADDR(bp, bno) ((bp)->b_maps[0].bm_bn = (xfs_daddr_t)(bno)) -static inline void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref) -{ - atomic_set(&bp->b_lru_ref, lru_ref); -} +void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref); static inline int xfs_buf_ispinned(struct xfs_buf *bp) { diff --git a/fs/xfs/xfs_error.c b/fs/xfs/xfs_error.c index eaf86f55b7f21..6732b0a0d8261 100644 --- a/fs/xfs/xfs_error.c +++ b/fs/xfs/xfs_error.c @@ -58,6 +58,7 @@ static unsigned int xfs_errortag_random_default[] = { XFS_RANDOM_DROP_WRITES, XFS_RANDOM_LOG_BAD_CRC, XFS_RANDOM_LOG_ITEM_PIN, + XFS_RANDOM_BUF_LRU_REF, }; struct xfs_errortag_attr { @@ -163,6 +164,7 @@ XFS_ERRORTAG_ATTR_RW(ag_resv_critical, XFS_ERRTAG_AG_RESV_CRITICAL); XFS_ERRORTAG_ATTR_RW(drop_writes, XFS_ERRTAG_DROP_WRITES); XFS_ERRORTAG_ATTR_RW(log_bad_crc, XFS_ERRTAG_LOG_BAD_CRC); XFS_ERRORTAG_ATTR_RW(log_item_pin, XFS_ERRTAG_LOG_ITEM_PIN); +XFS_ERRORTAG_ATTR_RW(buf_lru_ref, XFS_ERRTAG_BUF_LRU_REF); static struct attribute *xfs_errortag_attrs[] = { XFS_ERRORTAG_ATTR_LIST(noerror), @@ -196,6 +198,7 @@ static struct attribute *xfs_errortag_attrs[] = { XFS_ERRORTAG_ATTR_LIST(drop_writes), XFS_ERRORTAG_ATTR_LIST(log_bad_crc), XFS_ERRORTAG_ATTR_LIST(log_item_pin), + XFS_ERRORTAG_ATTR_LIST(buf_lru_ref), NULL, }; diff --git a/fs/xfs/xfs_error.h b/fs/xfs/xfs_error.h index 7c4bef3bddb75..78a7f43f8d018 100644 --- a/fs/xfs/xfs_error.h +++ b/fs/xfs/xfs_error.h @@ -107,7 +107,8 @@ extern void xfs_verifier_error(struct xfs_buf *bp); #define XFS_ERRTAG_DROP_WRITES 28 #define XFS_ERRTAG_LOG_BAD_CRC 29 #define XFS_ERRTAG_LOG_ITEM_PIN 30 -#define XFS_ERRTAG_MAX 31 +#define XFS_ERRTAG_BUF_LRU_REF 31 +#define XFS_ERRTAG_MAX 32 /* * Random factors for above tags, 1 means always, 2 means 1/2 time, etc. @@ -143,6 +144,7 @@ extern void xfs_verifier_error(struct xfs_buf *bp); #define XFS_RANDOM_DROP_WRITES 1 #define XFS_RANDOM_LOG_BAD_CRC 1 #define XFS_RANDOM_LOG_ITEM_PIN 1 +#define XFS_RANDOM_BUF_LRU_REF 2 #ifdef DEBUG extern int xfs_errortag_init(struct xfs_mount *mp); -- 2.39.5