| Message ID | 20180124032203.3dszkkof5f36qpmf@hungrycats.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Jan 23, 2018 at 10:22:09PM -0500, Zygo Blaxell wrote: >Until v4.14, this warning was very infrequent: > > WARNING: CPU: 3 PID: 18172 at fs/btrfs/backref.c:1391 find_parent_nodes+0xc41/0x14e0 > Modules linked in: [...] > CPU: 3 PID: 18172 Comm: bees Tainted: G D W L 4.11.9-zb64+ #1 > Hardware name: System manufacturer System Product Name/M5A78L-M/USB3, BIOS 2101 12/02/2014 > Call Trace: > dump_stack+0x85/0xc2 > __warn+0xd1/0xf0 > warn_slowpath_null+0x1d/0x20 > find_parent_nodes+0xc41/0x14e0 > __btrfs_find_all_roots+0xad/0x120 > ? extent_same_check_offsets+0x70/0x70 > iterate_extent_inodes+0x168/0x300 > iterate_inodes_from_logical+0x87/0xb0 > ? iterate_inodes_from_logical+0x87/0xb0 > ? extent_same_check_offsets+0x70/0x70 > btrfs_ioctl+0x8ac/0x2820 > ? lock_acquire+0xc2/0x200 > do_vfs_ioctl+0x91/0x700 > ? __fget+0x112/0x200 > SyS_ioctl+0x79/0x90 > entry_SYSCALL_64_fastpath+0x23/0xc6 > ? trace_hardirqs_off_caller+0x1f/0x140 > >Starting with v4.14 (specifically 86d5f9944252 ("btrfs: convert prelimary >reference tracking to use rbtrees")) the WARN_ON occurs three orders of >magnitude more frequently--almost once per second while running workloads >like bees. > >Replace the WARN_ON() with a comment rationale for its removal. >The rationale is paraphrased from an explanation by Edmund Nadolski ><enadolski@suse.de> on the linux-btrfs mailing list. > >Fixes: 8da6d5815c59 ("Btrfs: added btrfs_find_all_roots()") >Signed-off-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org> Reviewed-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
On Wed, Jan 24, 2018 at 11:33:08AM +0800, Lu Fengqi wrote: > On Tue, Jan 23, 2018 at 10:22:09PM -0500, Zygo Blaxell wrote: > >Until v4.14, this warning was very infrequent: > > > > WARNING: CPU: 3 PID: 18172 at fs/btrfs/backref.c:1391 find_parent_nodes+0xc41/0x14e0 > > Modules linked in: [...] > > CPU: 3 PID: 18172 Comm: bees Tainted: G D W L 4.11.9-zb64+ #1 > > Hardware name: System manufacturer System Product Name/M5A78L-M/USB3, BIOS 2101 12/02/2014 > > Call Trace: > > dump_stack+0x85/0xc2 > > __warn+0xd1/0xf0 > > warn_slowpath_null+0x1d/0x20 > > find_parent_nodes+0xc41/0x14e0 > > __btrfs_find_all_roots+0xad/0x120 > > ? extent_same_check_offsets+0x70/0x70 > > iterate_extent_inodes+0x168/0x300 > > iterate_inodes_from_logical+0x87/0xb0 > > ? iterate_inodes_from_logical+0x87/0xb0 > > ? extent_same_check_offsets+0x70/0x70 > > btrfs_ioctl+0x8ac/0x2820 > > ? lock_acquire+0xc2/0x200 > > do_vfs_ioctl+0x91/0x700 > > ? __fget+0x112/0x200 > > SyS_ioctl+0x79/0x90 > > entry_SYSCALL_64_fastpath+0x23/0xc6 > > ? trace_hardirqs_off_caller+0x1f/0x140 > > > >Starting with v4.14 (specifically 86d5f9944252 ("btrfs: convert prelimary > >reference tracking to use rbtrees")) the WARN_ON occurs three orders of > >magnitude more frequently--almost once per second while running workloads > >like bees. > > > >Replace the WARN_ON() with a comment rationale for its removal. > >The rationale is paraphrased from an explanation by Edmund Nadolski > ><enadolski@suse.de> on the linux-btrfs mailing list. > > > >Fixes: 8da6d5815c59 ("Btrfs: added btrfs_find_all_roots()") > >Signed-off-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org> > > Reviewed-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com> Added to next, thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c index 7d0dc100a09a..06597c5f9f4b 100644 --- a/fs/btrfs/backref.c +++ b/fs/btrfs/backref.c @@ -1263,7 +1263,16 @@ static int find_parent_nodes(struct btrfs_trans_handle *trans, while (node) { ref = rb_entry(node, struct prelim_ref, rbnode); node = rb_next(&ref->rbnode); - WARN_ON(ref->count < 0); + /* + * ref->count < 0 can happen here if there are delayed + * refs with a node->action of BTRFS_DROP_DELAYED_REF. + * prelim_ref_insert() relies on this when merging + * identical refs to keep the overall count correct. + * prelim_ref_insert() will merge only those refs + * which compare identically. Any refs having + * e.g. different offsets would not be merged, + * and would retain their original ref->count < 0. + */ if (roots && ref->count && ref->root_id && ref->parent == 0) { if (sc && sc->root_objectid && ref->root_id != sc->root_objectid) {
Until v4.14, this warning was very infrequent: WARNING: CPU: 3 PID: 18172 at fs/btrfs/backref.c:1391 find_parent_nodes+0xc41/0x14e0 Modules linked in: [...] CPU: 3 PID: 18172 Comm: bees Tainted: G D W L 4.11.9-zb64+ #1 Hardware name: System manufacturer System Product Name/M5A78L-M/USB3, BIOS 2101 12/02/2014 Call Trace: dump_stack+0x85/0xc2 __warn+0xd1/0xf0 warn_slowpath_null+0x1d/0x20 find_parent_nodes+0xc41/0x14e0 __btrfs_find_all_roots+0xad/0x120 ? extent_same_check_offsets+0x70/0x70 iterate_extent_inodes+0x168/0x300 iterate_inodes_from_logical+0x87/0xb0 ? iterate_inodes_from_logical+0x87/0xb0 ? extent_same_check_offsets+0x70/0x70 btrfs_ioctl+0x8ac/0x2820 ? lock_acquire+0xc2/0x200 do_vfs_ioctl+0x91/0x700 ? __fget+0x112/0x200 SyS_ioctl+0x79/0x90 entry_SYSCALL_64_fastpath+0x23/0xc6 ? trace_hardirqs_off_caller+0x1f/0x140 Starting with v4.14 (specifically 86d5f9944252 ("btrfs: convert prelimary reference tracking to use rbtrees")) the WARN_ON occurs three orders of magnitude more frequently--almost once per second while running workloads like bees. Replace the WARN_ON() with a comment rationale for its removal. The rationale is paraphrased from an explanation by Edmund Nadolski <enadolski@suse.de> on the linux-btrfs mailing list. Fixes: 8da6d5815c59 ("Btrfs: added btrfs_find_all_roots()") Signed-off-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org> --- v2: Replace WARN_ON with rationale instead of merely deleting it. Trim irrelevant detail from the backtrace. Add Fixes reference. Fix subject line (missing "< 0"). fs/btrfs/backref.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)