On Fri, Mar 21, 2014 at 09:48:50PM -0500, Eric Sandeen wrote: > 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: xfs_buf_iodone_work+0x0/0x1d0 [xfs] > > 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 > changes. > > 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 > --- a/fs/xfs/xfs_buf.c > +++ b/fs/xfs/xfs_buf.c > @@ -1361,21 +1361,29 @@ xfs_buf_iorequest( > xfs_buf_wait_unpin(bp); > xfs_buf_hold(bp); > > - /* 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. > */ > atomic_set(&bp->b_io_remaining, 1); > _xfs_buf_ioapply(bp); > - _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); > Out of curiosity, is there any major reason we don't use 0 here unconditionally? Are we worried about I/O completing before we have a chance to decrement the reference? Looks good to me either way: Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx> > xfs_buf_rele(bp); > } > > /* > * 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 which > + * case nothing will ever complete. It returns the I/O error code, if any, or > + * 0 if there was no error. > */ > int > xfs_buf_iowait( > > _______________________________________________ > xfs mailing list > xfs@xxxxxxxxxxx > http://oss.sgi.com/mailman/listinfo/xfs _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
