Re: [PATCH] xfs: remove b_last_holder & associated macros
From: Carlos Maiolino <hidden>
Date: 2018-08-13 10:25:12
On Fri, Aug 10, 2018 at 02:46:04PM -0500, Eric Sandeen wrote:
The old lock tracking infrastructure in xfs using the b_last_holder field seems to only be useful if you can get into the system with a debugger; it seems that the existing tracepoints would be the way to go these days, and this old infrastructure can be removed. Signed-off-by: Eric Sandeen <redacted> --- If I'm missing the usefulness of this, please speak up :)
The tracepoints already mention the task trying to lock/release the lock, so, yeah, I don't see much usability for it anymore. There is a single usage I could think of, which would be some deadlock in xfs_buf code, and forcing a crash and reading the b_last_holder from the vmcore would give some clue about the deadlock. But... For this to happen, the kernel running should be compiled with debug, so, it's not a production thing, and, if the problem could be reproduced, then, enabling the tracepoints will do the 'same' job. So, IMHO it's good to go. Reviewed-by: Carlos Maiolino <redacted>
quoted hunk ↗ jump to hunk
diff --git a/fs/xfs/xfs.h b/fs/xfs/xfs.h index 583a9f539bf1..f6ffb4f248f7 100644 --- a/fs/xfs/xfs.h +++ b/fs/xfs/xfs.h@@ -8,7 +8,6 @@ #ifdef CONFIG_XFS_DEBUG #define DEBUG 1 -#define XFS_BUF_LOCK_TRACKING 1 #endif #ifdef CONFIG_XFS_ASSERT_FATALdiff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index c641c7fa1a03..e839907e8492 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c@@ -34,16 +34,6 @@ static kmem_zone_t *xfs_buf_zone; -#ifdef XFS_BUF_LOCK_TRACKING -# define XB_SET_OWNER(bp) ((bp)->b_last_holder = current->pid) -# define XB_CLEAR_OWNER(bp) ((bp)->b_last_holder = -1) -# define XB_GET_OWNER(bp) ((bp)->b_last_holder) -#else -# define XB_SET_OWNER(bp) do { } while (0) -# define XB_CLEAR_OWNER(bp) do { } while (0) -# define XB_GET_OWNER(bp) do { } while (0) -#endif - #define xb_to_gfp(flags) \ ((((flags) & XBF_READ_AHEAD) ? __GFP_NORETRY : GFP_NOFS) | __GFP_NOWARN)@@ -226,7 +216,6 @@ _xfs_buf_alloc( INIT_LIST_HEAD(&bp->b_li_list); sema_init(&bp->b_sema, 0); /* held, no waiters */ spin_lock_init(&bp->b_lock); - XB_SET_OWNER(bp); bp->b_target = target; bp->b_flags = flags;@@ -1091,12 +1080,10 @@ xfs_buf_trylock( int locked; locked = down_trylock(&bp->b_sema) == 0; - if (locked) { - XB_SET_OWNER(bp); + if (locked) trace_xfs_buf_trylock(bp, _RET_IP_); - } else { + else trace_xfs_buf_trylock_fail(bp, _RET_IP_); - } return locked; }@@ -1118,7 +1105,6 @@ xfs_buf_lock( if (atomic_read(&bp->b_pin_count) && (bp->b_flags & XBF_STALE)) xfs_log_force(bp->b_target->bt_mount, 0); down(&bp->b_sema); - XB_SET_OWNER(bp); trace_xfs_buf_lock_done(bp, _RET_IP_); }@@ -1129,9 +1115,7 @@ xfs_buf_unlock( { ASSERT(xfs_buf_islocked(bp)); - XB_CLEAR_OWNER(bp); up(&bp->b_sema); - trace_xfs_buf_unlock(bp, _RET_IP_); }diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h index f04613181ca1..4e3171acd0f8 100644 --- a/fs/xfs/xfs_buf.h +++ b/fs/xfs/xfs_buf.h@@ -198,10 +198,6 @@ typedef struct xfs_buf { int b_last_error; const struct xfs_buf_ops *b_ops; - -#ifdef XFS_BUF_LOCK_TRACKING - int b_last_holder; -#endif } xfs_buf_t; /* Finding and Reading Buffers */
-- Carlos