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Message-ID: <Yh/Jl3wU+y1wRqRb@google.com>
Date: Wed, 2 Mar 2022 11:46:31 -0800
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...nel.org>
Cc: linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: avoid sb_start_intwrite during
eviction
On 03/02, Chao Yu wrote:
> On 2022/3/2 13:45, Jaegeuk Kim wrote:
> > On 03/01, Jaegeuk Kim wrote:
> > > On 03/01, Jaegeuk Kim wrote:
> > > > On 03/02, Chao Yu wrote:
> > > > > On 2022/3/1 12:48, Jaegeuk Kim wrote:
> > > > > > 1. waiting for f2fs_evict_inode
> > > > > > [ 5560.043945] __wait_on_freeing_inode+0xac/0xf0
> > > > > > [ 5560.045540] ? var_wake_function+0x30/0x30
> > > > > > [ 5560.047036] find_inode_fast+0x6d/0xc0
> > > > > > [ 5560.048473] iget_locked+0x79/0x230
> > > > > > [ 5560.049933] f2fs_iget+0x27/0x1200 [f2fs]
> > > > > > [ 5560.051496] f2fs_lookup+0x18c/0x3e0 [f2fs]
> > > > > > [ 5560.053069] __lookup_slow+0x84/0x150
> > > > > > [ 5560.054503] walk_component+0x141/0x1b0
> > > > > > [ 5560.055938] link_path_walk.part.0+0x23b/0x360
> > > > > > [ 5560.057541] ? end_bio_bh_io_sync+0x37/0x50
> > > > > > [ 5560.059086] path_parentat+0x3c/0x90
> > > > > > [ 5560.060492] filename_parentat+0xd7/0x1e0
> > > > > > [ 5560.062002] ? blk_mq_free_request+0x127/0x150
> > > > > > [ 5560.063576] do_renameat2+0xc1/0x5b0
> > > > > > --> sb_start_write(m->mnt_sb); -> __sb_start_write(sb, SB_FREEZE_WRITE);
> > > > > >
> > > > > > [ 5560.064999] ? __check_object_size+0x13f/0x150
> > > > > > [ 5560.066559] ? strncpy_from_user+0x44/0x150
> > > > > > [ 5560.068038] ? getname_flags.part.0+0x4c/0x1b0
> > > > > > [ 5560.069617] __x64_sys_renameat2+0x51/0x60
> > > > > >
> > > > > > 2. waiting for sb_start_intwrite -> __sb_start_write(sb, SB_FREEZE_FS);
> > > > >
> > > > > It's still not clear that why __sb_start_write(sb, SB_FREEZE_FS) will be blocked,
> > > > > as SB_FREEZE_FS and SB_FREEZE_WRITE points to different locks.
> > > >
> > > > It seems I missed another call, thaw_super(), got SB_FREEZE_FS and then being
> > > > stuck to grab SB_FREEZE_WRITE.
> > >
> > > Ah, sorry. freeze_super().
> >
> > Messed up. So, the lock order is SB_FREEZE_WRITE -> SB_FREEZE_FS in both cases.
>
> Yeah, I noticed this, w/ such lock order, Thread C (freeze_super) will be blocked
> on SB_FREEZE_WRITE, and then Thread B won't be block on SB_FREEZE_FS, right?
Yeah, checking the code path again.
>
> Thanks,
>
> >
> > >
> > > >
> > > > >
> > > > > Thread A Thread B Thread C
> > > > > - rename
> > > > > - sb_start_write
> > > > > - __sb_start_write(SB_FREEZE_WRITE)
> > > > > ...
> > > > > - f2fs_lookup
> > > > > ...
> > > > > - __wait_on_freeing_inode
> > > > > - drop_slab
> > > > > - prune_icache_sb
> > > > > - inode_lru_isolate
> > > > > :inode->i_state |= I_FREEING
> > > > > - Is there any flow that it has already held
> > > > > SB_FREEZE_FS and try to lock SB_FREEZE_WRITE?
> > > > > - f2fs_evict_inode
> > > > > - __sb_start_write(SB_FREEZE_FS)
> > > > >
> > > > > Thanks,
> > > > >
> > > > > >
> > > > > > [ 5560.152447] percpu_rwsem_wait+0xaf/0x160
> > > > > > [ 5560.154000] ? percpu_down_write+0xd0/0xd0
> > > > > > [ 5560.155498] __percpu_down_read+0x4e/0x60
> > > > > > [ 5560.157000] f2fs_evict_inode+0x5a3/0x610 [f2fs]
> > > > > > [ 5560.158648] ? var_wake_function+0x30/0x30
> > > > > > [ 5560.160341] evict+0xd2/0x180
> > > > > > [ 5560.161728] prune_icache_sb+0x81/0xb0
> > > > > > --> inode_lru_isolate() -> inode->i_state |= I_FREEING;
> > > > > >
> > > > > > [ 5560.163179] super_cache_scan+0x169/0x1f0
> > > > > > [ 5560.164675] do_shrink_slab+0x145/0x2b0
> > > > > > [ 5560.166121] shrink_slab+0x186/0x2d0
> > > > > > [ 5560.167481] drop_slab_node+0x4a/0x90
> > > > > > [ 5560.168876] drop_slab+0x3e/0x80
> > > > > > [ 5560.170178] drop_caches_sysctl_handler+0x75/0x90
> > > > > > [ 5560.171761] proc_sys_call_handler+0x149/0x280
> > > > > > [ 5560.173328] proc_sys_write+0x13/0x20
> > > > > > [ 5560.174667] new_sync_write+0x117/0x1b0
> > > > > > [ 5560.176120] vfs_write+0x1d5/0x270
> > > > > > [ 5560.177409] ksys_write+0x67/0xe0
> > > > > >
> > > > > > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > > > > > ---
> > > > > > Note, I found this call stack.
> > > > > >
> > > > > > fs/f2fs/inode.c | 2 --
> > > > > > 1 file changed, 2 deletions(-)
> > > > > >
> > > > > > diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> > > > > > index ab8e0c06c78c..882db4bd917b 100644
> > > > > > --- a/fs/f2fs/inode.c
> > > > > > +++ b/fs/f2fs/inode.c
> > > > > > @@ -778,7 +778,6 @@ void f2fs_evict_inode(struct inode *inode)
> > > > > > f2fs_remove_ino_entry(sbi, inode->i_ino, UPDATE_INO);
> > > > > > f2fs_remove_ino_entry(sbi, inode->i_ino, FLUSH_INO);
> > > > > > - sb_start_intwrite(inode->i_sb);
> > > > > > set_inode_flag(inode, FI_NO_ALLOC);
> > > > > > i_size_write(inode, 0);
> > > > > > retry:
> > > > > > @@ -809,7 +808,6 @@ void f2fs_evict_inode(struct inode *inode)
> > > > > > if (dquot_initialize_needed(inode))
> > > > > > set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
> > > > > > }
> > > > > > - sb_end_intwrite(inode->i_sb);
> > > > > > no_delete:
> > > > > > dquot_drop(inode);
> > > >
> > > >
> > > > _______________________________________________
> > > > Linux-f2fs-devel mailing list
> > > > Linux-f2fs-devel@...ts.sourceforge.net
> > > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> > >
> > >
> > > _______________________________________________
> > > Linux-f2fs-devel mailing list
> > > Linux-f2fs-devel@...ts.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
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