When testing exhaustion of dm snapshots, the following appeared
with CONFIG_DEBUG_OBJECTS_FREE enabled:
ODEBUG: free active (active state 0) object type: work_struct hint:
indicating that we'd freed a buffer which still had a pending reference,
down this path:
[ 190.867975] [<ffffffff8133e6fb>] debug_check_no_obj_freed+0x22b/0x270
[ 190.880820] [<ffffffff811da1d0>] kmem_cache_free+0xd0/0x370
[ 190.892615] [<ffffffffa02c5924>] xfs_buf_free+0xe4/0x210 [xfs]
[ 190.905629] [<ffffffffa02c6167>] xfs_buf_rele+0xe7/0x270 [xfs]
[ 190.911770] [<ffffffffa034c826>] xfs_trans_read_buf_map+0x7b6/0xac0 [xfs]
At issue is the fact that if IO fails in xfs_buf_iorequest,
we'll queue completion unconditionally, and then call
xfs_buf_rele; but if IO failed, there are no IOs remaining,
and xfs_buf_rele will free the bp while work is still queued.
Fix this by not scheduling completion if the buffer has
an error on it; run it immediately. The rest is only comment
Thanks to dchinner for spotting the root cause.
Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
p.s. or maybe this could be moved into _xfs_buf_ioend ...
I think I see some nice cleanups for xfs_buf_ioend vs.
_xfs_buf_ioend w.r.t. when "schedule" is true, so maybe
I can clean it up then.
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 9c061ef..45eb5ef 100644
@@ -1361,21 +1361,29 @@ xfs_buf_iorequest(
- /* Set the count to 1 initially, this will stop an I/O
+ * Set the count to 1 initially, this will stop an I/O
* completion callout which happens before we have started
* all the I/O from calling xfs_buf_ioend too early.
- _xfs_buf_ioend(bp, 1);
+ * If _xfs_buf_ioapply failed, we'll get back here with
+ * only the reference we took above. _xfs_buf_ioend will
+ * drop it to zero, so we'd better not queue it for later,
+ * or we'll free it before it's done.
+ _xfs_buf_ioend(bp, bp->b_error ? 0 : 1);
* Waits for I/O to complete on the buffer supplied. It returns immediately if
- * no I/O is pending or there is already a pending error on the buffer. It
- * returns the I/O error code, if any, or 0 if there was no error.
+ * no I/O is pending or there is already a pending error on the buffer, in
+ * case nothing will ever complete. It returns the I/O error code, if any, or
+ * 0 if there was no error.