On Tue 16-06-20 17:39:33, Yafang Shao wrote: > On Tue, Jun 16, 2020 at 5:27 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > On Tue 16-06-20 17:05:25, Yafang Shao wrote: > > > On Tue, Jun 16, 2020 at 4:16 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > > On Mon 15-06-20 07:56:21, Yafang Shao wrote: > > > > > Recently there is a XFS deadlock on our server with an old kernel. > > > > > This deadlock is caused by allocating memory in xfs_map_blocks() while > > > > > doing writeback on behalf of memroy reclaim. Although this deadlock happens > > > > > on an old kernel, I think it could happen on the upstream as well. This > > > > > issue only happens once and can't be reproduced, so I haven't tried to > > > > > reproduce it on upsteam kernel. > > > > > > > > > > Bellow is the call trace of this deadlock. > > > > > [480594.790087] INFO: task redis-server:16212 blocked for more than 120 seconds. > > > > > [480594.790087] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > > > > > [480594.790088] redis-server D ffffffff8168bd60 0 16212 14347 0x00000004 > > > > > [480594.790090] ffff880da128f070 0000000000000082 ffff880f94a2eeb0 ffff880da128ffd8 > > > > > [480594.790092] ffff880da128ffd8 ffff880da128ffd8 ffff880f94a2eeb0 ffff88103f9d6c40 > > > > > [480594.790094] 0000000000000000 7fffffffffffffff ffff88207ffc0ee8 ffffffff8168bd60 > > > > > [480594.790096] Call Trace: > > > > > [480594.790101] [<ffffffff8168dce9>] schedule+0x29/0x70 > > > > > [480594.790103] [<ffffffff8168b749>] schedule_timeout+0x239/0x2c0 > > > > > [480594.790111] [<ffffffff8168d28e>] io_schedule_timeout+0xae/0x130 > > > > > [480594.790114] [<ffffffff8168d328>] io_schedule+0x18/0x20 > > > > > [480594.790116] [<ffffffff8168bd71>] bit_wait_io+0x11/0x50 > > > > > [480594.790118] [<ffffffff8168b895>] __wait_on_bit+0x65/0x90 > > > > > [480594.790121] [<ffffffff811814e1>] wait_on_page_bit+0x81/0xa0 > > > > > [480594.790125] [<ffffffff81196ad2>] shrink_page_list+0x6d2/0xaf0 > > > > > [480594.790130] [<ffffffff811975a3>] shrink_inactive_list+0x223/0x710 > > > > > [480594.790135] [<ffffffff81198225>] shrink_lruvec+0x3b5/0x810 > > > > > [480594.790139] [<ffffffff8119873a>] shrink_zone+0xba/0x1e0 > > > > > [480594.790141] [<ffffffff81198c20>] do_try_to_free_pages+0x100/0x510 > > > > > [480594.790143] [<ffffffff8119928d>] try_to_free_mem_cgroup_pages+0xdd/0x170 > > > > > [480594.790145] [<ffffffff811f32de>] mem_cgroup_reclaim+0x4e/0x120 > > > > > [480594.790147] [<ffffffff811f37cc>] __mem_cgroup_try_charge+0x41c/0x670 > > > > > [480594.790153] [<ffffffff811f5cb6>] __memcg_kmem_newpage_charge+0xf6/0x180 > > > > > [480594.790157] [<ffffffff8118c72d>] __alloc_pages_nodemask+0x22d/0x420 > > > > > [480594.790162] [<ffffffff811d0c7a>] alloc_pages_current+0xaa/0x170 > > > > > [480594.790165] [<ffffffff811db8fc>] new_slab+0x30c/0x320 > > > > > [480594.790168] [<ffffffff811dd17c>] ___slab_alloc+0x3ac/0x4f0 > > > > > [480594.790204] [<ffffffff81685656>] __slab_alloc+0x40/0x5c > > > > > [480594.790206] [<ffffffff811dfc43>] kmem_cache_alloc+0x193/0x1e0 > > > > > [480594.790233] [<ffffffffa04fab67>] kmem_zone_alloc+0x97/0x130 [xfs] > > > > > [480594.790247] [<ffffffffa04f90ba>] _xfs_trans_alloc+0x3a/0xa0 [xfs] > > > > > [480594.790261] [<ffffffffa04f915c>] xfs_trans_alloc+0x3c/0x50 [xfs] > > > > > > > > Now with a more explanation from Dave I have got back to the original > > > > backtrace. Not sure which kernel version you are using but this path > > > > should have passed xfs_trans_reserve which sets PF_MEMALLOC_NOFS and > > > > this in turn should have made __alloc_pages_nodemask to use __GFP_NOFS > > > > and the memcg reclaim shouldn't ever wait_on_page_writeback (pressumably > > > > this is what the io_schedule is coming from). > > > > > > Hi Michal, > > > > > > The page is allocated before calling xfs_trans_reserve, so the > > > PF_MEMALLOC_NOFS hasn't been set yet. > > > See bellow, > > > > > > xfs_trans_alloc > > > kmem_zone_zalloc() <<< GPF_NOFS hasn't been set yet, but it may > > > trigger memory reclaim > > > xfs_trans_reserve() <<<< GPF_NOFS is set here (for the kernel > > > prior to commit 9070733b4efac, it is PF_FSTRANS) > > > > You are right, I have misread the actual allocation side. 8683edb7755b8 > > has added KM_NOFS and 73d30d48749f8 has removed it. I cannot really > > judge the correctness here. > > > > The history is complicated, but it doesn't matter. > Let's turn back to the upstream kernel now. As I explained in the commit log, > xfs_vm_writepages > -> iomap_writepages. > -> write_cache_pages > -> lock_page <<<< This page is locked. > -> writepages ( which is iomap_do_writepage) > -> xfs_map_blocks > -> xfs_convert_blocks > -> xfs_bmapi_convert_delalloc > -> xfs_trans_alloc > -> kmem_zone_zalloc //It should alloc page > with GFP_NOFS > > If GFP_NOFS isn't set in xfs_trans_alloc(), the kmem_zone_zalloc() may > trigger the memory reclaim then it may wait on the page locked in > write_cache_pages() ... This cannot happen because the memory reclaim backs off on locked pages. Have a look at trylock_page at the very beginning of the shrink_page_list loop. You are likely waiting on a different page which is not being flushed because of the FS ordering requirement or something like that. > That means the ->writepages should be set with GFP_NOFS to avoid this > recursive filesystem reclaim. -- Michal Hocko SUSE Labs
