Messages in this thread Patch in this message | | | Date | Wed, 13 Apr 2022 19:42:47 -0700 | From | Jaegeuk Kim <> | Subject | Re: [PATCH] f2fs: avoid deadlock in gc thread under low memory |
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On 04/14, Wu Yan wrote: > On 4/14/22 10:18, Jaegeuk Kim wrote: > > On 04/14, Wu Yan wrote: > > > On 4/14/22 01:00, Jaegeuk Kim wrote: > > > > On 04/13, Rokudo Yan wrote: > > > > > There is a potential deadlock in gc thread may happen > > > > > under low memory as below: > > > > > > > > > > gc_thread_func > > > > > -f2fs_gc > > > > > -do_garbage_collect > > > > > -gc_data_segment > > > > > -move_data_block > > > > > -set_page_writeback(fio.encrypted_page); > > > > > -f2fs_submit_page_write > > > > > as f2fs_submit_page_write try to do io merge when possible, so the > > > > > encrypted_page is marked PG_writeback but may not submit to block > > > > > layer immediately, if system enter low memory when gc thread try > > > > > to move next data block, it may do direct reclaim and enter fs layer > > > > > as below: > > > > > -move_data_block > > > > > -f2fs_grab_cache_page(index=?, for_write=false) > > > > > -grab_cache_page > > > > > -find_or_create_page > > > > > -pagecache_get_page > > > > > -__page_cache_alloc -- __GFP_FS is set > > > > > -alloc_pages_node > > > > > -__alloc_pages > > > > > -__alloc_pages_slowpath > > > > > -__alloc_pages_direct_reclaim > > > > > -__perform_reclaim > > > > > -try_to_free_pages > > > > > -do_try_to_free_pages > > > > > -shrink_zones > > > > > -mem_cgroup_soft_limit_reclaim > > > > > -mem_cgroup_soft_reclaim > > > > > -mem_cgroup_shrink_node > > > > > -shrink_node_memcg > > > > > -shrink_list > > > > > -shrink_inactive_list > > > > > -shrink_page_list > > > > > -wait_on_page_writeback -- the page is marked > > > > > writeback during previous move_data_block call > > > > > > > > > > the gc thread wait for the encrypted_page writeback complete, > > > > > but as gc thread held sbi->gc_lock, the writeback & sync thread > > > > > may blocked waiting for sbi->gc_lock, so the bio contain the > > > > > encrypted_page may nerver submit to block layer and complete the > > > > > writeback, which cause deadlock. To avoid this deadlock condition, > > > > > we mark the gc thread with PF_MEMALLOC_NOFS flag, then it will nerver > > > > > enter fs layer when try to alloc cache page during move_data_block. > > > > > > > > > > Signed-off-by: Rokudo Yan <wu-yan@tcl.com> > > > > > --- > > > > > fs/f2fs/gc.c | 6 ++++++ > > > > > 1 file changed, 6 insertions(+) > > > > > > > > > > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c > > > > > index e020804f7b07..cc71f77b98c8 100644 > > > > > --- a/fs/f2fs/gc.c > > > > > +++ b/fs/f2fs/gc.c > > > > > @@ -38,6 +38,12 @@ static int gc_thread_func(void *data) > > > > > wait_ms = gc_th->min_sleep_time; > > > > > + /* > > > > > + * Make sure that no allocations from gc thread will ever > > > > > + * recurse to the fs layer to avoid deadlock as it will > > > > > + * hold sbi->gc_lock during garbage collection > > > > > + */ > > > > > + memalloc_nofs_save(); > > > > > > > > I think this cannot cover all the f2fs_gc() call cases. Can we just avoid by: > > > > > > > > --- a/fs/f2fs/gc.c > > > > +++ b/fs/f2fs/gc.c > > > > @@ -1233,7 +1233,7 @@ static int move_data_block(struct inode *inode, block_t bidx, > > > > CURSEG_ALL_DATA_ATGC : CURSEG_COLD_DATA; > > > > > > > > /* do not read out */ > > > > - page = f2fs_grab_cache_page(inode->i_mapping, bidx, false); > > > > + page = f2fs_grab_cache_page(inode->i_mapping, bidx, true); > > > > if (!page) > > > > return -ENOMEM; > > > > > > > > Thanks, > > > > > > > > > set_freezable(); > > > > > do { > > > > > bool sync_mode, foreground = false; > > > > > -- > > > > > 2.25.1 > > > > > > Hi, Jaegeuk > > > > > > I'm not sure if any other case may trigger the issue, but the stack traces I > > > have caught so far are all the same as below: > > > > > > f2fs_gc-253:12 D 226966.808196 572 302561 150976 0x1200840 0x0 572 > > > 237207473347056 > > > <ffffff889d88668c> __switch_to+0x134/0x150 > > > <ffffff889e764b6c> __schedule+0xd5c/0x1100 > > > <ffffff889e76554c> io_schedule+0x90/0xc0 > > > <ffffff889d9fb880> wait_on_page_bit+0x194/0x208 > > > <ffffff889da167b4> shrink_page_list+0x62c/0xe74 > > > <ffffff889da1d354> shrink_inactive_list+0x2c0/0x698 > > > <ffffff889da181f4> shrink_node_memcg+0x3dc/0x97c > > > <ffffff889da17d44> mem_cgroup_shrink_node+0x144/0x218 > > > <ffffff889da6610c> mem_cgroup_soft_limit_reclaim+0x188/0x47c > > > <ffffff889da17a40> do_try_to_free_pages+0x204/0x3a0 > > > <ffffff889da176c8> try_to_free_pages+0x35c/0x4d0 > > > <ffffff889da05d60> __alloc_pages_nodemask+0x7a4/0x10d0 > > > <ffffff889d9fc82c> pagecache_get_page+0x184/0x2ec > > > > Is this deadlock trying to grab a lock, instead of waiting for writeback? > > Could you share all the backtraces of the tasks? > > > > For writeback above, looking at the code, f2fs_gc uses three mappings, meta, > > node, and data, and meta/node inodes are masking GFP_NOFS in f2fs_iget(), > > while data inode does not. So, the above f2fs_grab_cache_page() in > > move_data_block() is actually calling w/o NOFS. > > > > > <ffffff889dbf8860> do_garbage_collect+0xfe0/0x2828 > > > <ffffff889dbf7434> f2fs_gc+0x4a0/0x8ec > > > <ffffff889dbf6bf4> gc_thread_func+0x240/0x4d4 > > > <ffffff889d8de9b0> kthread+0x17c/0x18c > > > <ffffff889d88567c> ret_from_fork+0x10/0x18 > > > > > > Thanks > > > yanwu > > Hi, Jaegeuk > > The gc thread is blocked on wait_on_page_writeback(encrypted page submit > before) when it try grab data inode page, the parsed stack traces as below: > > ppid=572 pid=572 D cpu=1 prio=120 wait=378s f2fs_gc-253:12 > Native callstack: > vmlinux wait_on_page_bit_common(page=0xFFFFFFBF7D2CD700, state=2, > lock=false) + 304 <mm/filemap.c:1035> > vmlinux wait_on_page_bit(page=0xFFFFFFBF7D2CD700, bit_nr=15) + 400 > > <mm/filemap.c:1074> > vmlinux wait_on_page_writeback(page=0xFFFFFFBF7D2CD700) + 36 > > <include/linux/pagemap.h:557> > vmlinux shrink_page_list(page_list=0xFFFFFF8011E83418, > pgdat=contig_page_data, sc=0xFFFFFF8011E835B8, ttu_flags=0, > stat=0xFFFFFF8011E833F0, force_reclaim=false) + 1576 <mm/vmscan.c:1171> > vmlinux shrink_inactive_list(lruvec=0xFFFFFFE003C304C0, > sc=0xFFFFFF8011E835B8, lru=LRU_INACTIVE_FILE) + 700 > <mm/vmscan.c:1966> > vmlinux shrink_list(lru=LRU_INACTIVE_FILE, lruvec=0xFFFFFF8011E834B8, > sc=0xFFFFFF8011E835B8) + 128 <mm/vmscan.c:2350> > vmlinux shrink_node_memcg(pgdat=contig_page_data, > memcg=0xFFFFFFE003C1A300, sc=0xFFFFFF8011E835B8, > lru_pages=0xFFFFFF8011E835B0) + 984 <mm/vmscan.c:2726> > vmlinux mem_cgroup_shrink_node(memcg=0xFFFFFFE003C1A300, > gfp_mask=21102794, noswap=false, pgdat=contig_page_data, > nr_scanned=0xFFFFFF8011E836A0) + 320 <mm/vmscan.c:3416> > vmlinux mem_cgroup_soft_reclaim(root_memcg=0xFFFFFFE003C1A300, > pgdat=contig_page_data) + 164 > <mm/memcontrol.c:1643> > vmlinux mem_cgroup_soft_limit_reclaim(pgdat=contig_page_data, order=0, > gfp_mask=21102794, total_scanned=0xFFFFFF8011E83720) + 388 > <mm/memcontrol.c:2913> > vmlinux shrink_zones(zonelist=contig_page_data + 14784, > sc=0xFFFFFF8011E83790) + 352 > <mm/vmscan.c:3094> > vmlinux do_try_to_free_pages(zonelist=contig_page_data + 14784, > sc=0xFFFFFF8011E83790) + 512 > <mm/vmscan.c:3164> > vmlinux try_to_free_pages(zonelist=contig_page_data + 14784, order=0, > gfp_mask=21102794, nodemask=0) + 856 > <mm/vmscan.c:3370> > vmlinux __perform_reclaim(gfp_mask=300431548, order=0, > ac=0xFFFFFF8011E83900) + 60 > <mm/page_alloc.c:3831> > vmlinux __alloc_pages_direct_reclaim(gfp_mask=300431548, order=0, > alloc_flags=300431604, ac=0xFFFFFF8011E83900) + 60 > <mm/page_alloc.c:3853> > vmlinux __alloc_pages_slowpath(gfp_mask=300431548, order=0, > ac=0xFFFFFF8011E83900) + 1244 > <mm/page_alloc.c:4240> > vmlinux __alloc_pages_nodemask() + 1952 > > <mm/page_alloc.c:4463> > vmlinux __alloc_pages(gfp_mask=21102794, order=0, preferred_nid=0) + 16 > <include/linux/gfp.h:515> > vmlinux __alloc_pages_node(nid=0, gfp_mask=21102794, order=0) + 16 > > <include/linux/gfp.h:528> > vmlinux alloc_pages_node(nid=0, gfp_mask=21102794, order=0) + 16 > > <include/linux/gfp.h:542> > vmlinux __page_cache_alloc(gfp=21102794) + 16 > > <include/linux/pagemap.h:226> > vmlinux pagecache_get_page() + 384 > > <mm/filemap.c:1520> > vmlinux find_or_create_page(offset=209) + 112 > > <include/linux/pagemap.h:333> > vmlinux grab_cache_page(index=209) + 112 > > <include/linux/pagemap.h:399> > vmlinux f2fs_grab_cache_page(index=209, for_write=false) + 112
Ok, I think this should be enough.
--- a/fs/f2fs/gc.c +++ b/fs/f2fs/gc.c @@ -1233,7 +1233,7 @@ static int move_data_block(struct inode *inode, block_t bidx, CURSEG_ALL_DATA_ATGC : CURSEG_COLD_DATA;
/* do not read out */ - page = f2fs_grab_cache_page(inode->i_mapping, bidx, false); + page = f2fs_grab_cache_page(inode->i_mapping, bidx, true); if (!page) return -ENOMEM;
> <fs/f2fs/f2fs.h:2429> > vmlinux move_data_block(inode=0xFFFFFFDFD578EEA0, gc_type=300432152, > segno=21904, off=145) + 3584 <fs/f2fs/gc.c:1119> > vmlinux gc_data_segment(sbi=0xFFFFFFE007C03000, sum=0xFFFFFF8011E83B10, > gc_list=0xFFFFFF8011E83AB8, segno=21904, gc_type=300432152) + 3644 > <fs/f2fs/gc.c:1475> > vmlinux do_garbage_collect(sbi=0xFFFFFFE007C03000, start_segno=21904, > gc_list=0xFFFFFF8011E83CF0, gc_type=0) + 4060 > <fs/f2fs/gc.c:1592> > vmlinux f2fs_gc(sbi=0xFFFFFFE007C03000, background=true, segno=4294967295) > + 1180 <fs/f2fs/gc.c:1684> > vmlinux gc_thread_func(data=0xFFFFFFE007C03000) + 572 > > <fs/f2fs/gc.c:118> > vmlinux kthread() + 376 > > <kernel/kthread.c:232> > vmlinux ret_from_fork() + > > Thanks > yanwu
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