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Date: Sat, 9 Jul 2016 09:22:58 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...nel.org>
Cc: linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, Chao Yu <yuchao0@...wei.com>
Subject: Re: [PATCH v3] f2fs: fix to avoid data update racing between GC and
DIO
On Fri, Jul 08, 2016 at 11:50:02PM +0800, Chao Yu wrote:
> Hi Jaegeuk,
>
> On 2016/7/8 11:19, Jaegeuk Kim wrote:
> > Hi Chao,
> >
> > Could you take a look at this in xfstests/generic/013?
> >
> > [ 502.480850] ======================================================
> > [ 502.480864] [ INFO: possible circular locking dependency detected ]
> > [ 502.480877] 4.7.0-rc1+ #124 Tainted: G OE
> > [ 502.480886] -------------------------------------------------------
> > [ 502.480897] fsstress/10729 is trying to acquire lock:
> > [ 502.480906] (&sb->s_type->i_mutex_key#18){+.+.+.}, at: [<ffffffff81299c3b>] do_blockdev_direct_IO+0x1db/0x2310
> > [ 502.480948]
> > [ 502.480948] but task is already holding lock:
> > [ 502.480959] (&fi->dio_rwsem){.+.+.+}, at: [<ffffffffc081e2b1>] f2fs_direct_IO+0xd1/0x3d0 [f2fs]
> > [ 502.481003]
> > [ 502.481003] which lock already depends on the new lock.
> > [ 502.481003]
> > [ 502.481018]
> > [ 502.481018] the existing dependency chain (in reverse order) is:
> > [ 502.481030]
> > [ 502.481030] -> #1 (&fi->dio_rwsem){.+.+.+}:
> > [ 502.481054] [<ffffffff810e51c3>] lock_acquire+0xd3/0x220
> > [ 502.481071] [<ffffffff818d1921>] down_read+0x51/0xa0
> > [ 502.481089] [<ffffffffc081e2b1>] f2fs_direct_IO+0xd1/0x3d0 [f2fs]
> > [ 502.481114] [<ffffffff811c34c7>] generic_file_direct_write+0xa7/0x160
> > [ 502.481133] [<ffffffff811c363d>] __generic_file_write_iter+0xbd/0x1e0
> > [ 502.481149] [<ffffffffc080437b>] f2fs_file_write_iter+0xdb/0x100 [f2fs]
> > [ 502.481173] [<ffffffff81253a88>] __vfs_write+0xc8/0x140
> > [ 502.481190] [<ffffffff81254c55>] vfs_write+0xb5/0x1b0
> > [ 502.481205] [<ffffffff81255fe9>] SyS_write+0x49/0xa0
> > [ 502.481220] [<ffffffff818d4100>] entry_SYSCALL_64_fastpath+0x23/0xc1
> > [ 502.481236]
> > [ 502.481236] -> #0 (&sb->s_type->i_mutex_key#18){+.+.+.}:
> > [ 502.481264] [<ffffffff810e481c>] __lock_acquire+0x161c/0x1940
> > [ 502.481280] [<ffffffff810e51c3>] lock_acquire+0xd3/0x220
> > [ 502.481296] [<ffffffff818d1b9a>] down_write+0x5a/0xc0
> > [ 502.481312] [<ffffffff81299c3b>] do_blockdev_direct_IO+0x1db/0x2310
> > [ 502.481328] [<ffffffff8129bdaa>] __blockdev_direct_IO+0x3a/0x40
> > [ 502.481344] [<ffffffffc081e2e4>] f2fs_direct_IO+0x104/0x3d0 [f2fs]
> > [ 502.481368] [<ffffffff811c40a9>] generic_file_read_iter+0x689/0x7e0
> > [ 502.481384] [<ffffffff812545d1>] __vfs_read+0xc1/0x130
> > [ 502.481399] [<ffffffff81254af1>] vfs_read+0x91/0x140
> > [ 502.481414] [<ffffffff81255f49>] SyS_read+0x49/0xa0
> > [ 502.481429] [<ffffffff818d4100>] entry_SYSCALL_64_fastpath+0x23/0xc1
> > [ 502.481445]
> > [ 502.481445] other info that might help us debug this:
> > [ 502.481445]
> > [ 502.481459] Possible unsafe locking scenario:
> > [ 502.481459]
> > [ 502.481726] CPU0 CPU1
> > [ 502.481987] ---- ----
> > [ 502.482242] lock(&fi->dio_rwsem);
> > [ 502.482501] lock(&sb->s_type->i_mutex_key#18);
> > [ 502.482765] lock(&fi->dio_rwsem);
> > [ 502.483025] lock(&sb->s_type->i_mutex_key#18);
>
> Seems we will suffer ABBA deadlock:
>
> writer reader
> - f2fs_file_write_iter
> - down_write(&inode->i_rwsem)
> - __generic_file_write_iter
> - generic_file_direct_write
> - f2fs_direct_IO
> - generic_file_read_iter
> - f2fs_direct_IO
> - down_read(&fi->dio_rwsem)
> - __blockdev_direct_IO
> - do_blockdev_direct_IO
> - down_write(&inode->i_rwsem)
>
> - down_read(&fi->dio_rwsem)
>
> What about splitting dio_rwsem to rdio_rwsem/wdio_rwsem for reader/writer to
> avoid deadlock?
Hmm, how about inode_trylock in GC?
>
> Thanks,
>
> > [ 502.483285]
> > [ 502.483285] *** DEADLOCK ***
> > [ 502.483285]
> > [ 502.484018] 1 lock held by fsstress/10729:
> > [ 502.484262] #0: (&fi->dio_rwsem){.+.+.+}, at: [<ffffffffc081e2b1>] f2fs_direct_IO+0xd1/0x3d0 [f2fs]
> >
> > Thanks,
> >
> > On Thu, Jul 07, 2016 at 12:49:12PM +0800, Chao Yu wrote:
> >> From: Chao Yu <yuchao0@...wei.com>
> >>
> >> Datas in file can be operated by GC and DIO simultaneously, so we will
> >> face race case as below:
> >>
> >> For write case:
> >> Thread A Thread B
> >> - generic_file_direct_write
> >> - invalidate_inode_pages2_range
> >> - f2fs_direct_IO
> >> - do_blockdev_direct_IO
> >> - do_direct_IO
> >> - get_more_blocks
> >> - f2fs_gc
> >> - do_garbage_collect
> >> - gc_data_segment
> >> - move_data_page
> >> - do_write_data_page
> >> migrate data block to new block address
> >> - dio_bio_submit
> >> update user data to old block address
> >>
> >> For read case:
> >> Thread A Thread B
> >> - generic_file_direct_write
> >> - invalidate_inode_pages2_range
> >> - f2fs_direct_IO
> >> - do_blockdev_direct_IO
> >> - do_direct_IO
> >> - get_more_blocks
> >> - f2fs_balance_fs
> >> - f2fs_gc
> >> - do_garbage_collect
> >> - gc_data_segment
> >> - move_data_page
> >> - do_write_data_page
> >> migrate data block to new block address
> >> - write_checkpoint
> >> - do_checkpoint
> >> - clear_prefree_segments
> >> - f2fs_issue_discard
> >> discard old block adress
> >> - dio_bio_submit
> >> update user buffer from obsolete block address
> >>
> >> In order to fix this, for one file, we should let DIO and GC getting exclusion
> >> against with each other.
> >>
> >> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> >> ---
> >> v3: use semaphore to avoid racing in between read dio and write dio.
> >> fs/f2fs/data.c | 4 ++++
> >> fs/f2fs/f2fs.h | 1 +
> >> fs/f2fs/gc.c | 13 +++++++++++++
> >> fs/f2fs/super.c | 1 +
> >> 4 files changed, 19 insertions(+)
> >>
> >> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >> index b6fd5bd..19197bb 100644
> >> --- a/fs/f2fs/data.c
> >> +++ b/fs/f2fs/data.c
> >> @@ -1712,6 +1712,7 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> >> {
> >> struct address_space *mapping = iocb->ki_filp->f_mapping;
> >> struct inode *inode = mapping->host;
> >> + struct f2fs_inode_info *fi = F2FS_I(inode);
> >> size_t count = iov_iter_count(iter);
> >> loff_t offset = iocb->ki_pos;
> >> int err;
> >> @@ -1727,7 +1728,10 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> >>
> >> trace_f2fs_direct_IO_enter(inode, offset, count, iov_iter_rw(iter));
> >>
> >> + down_read(&fi->dio_rwsem);
> >> err = blockdev_direct_IO(iocb, inode, iter, get_data_block_dio);
> >> + up_read(&fi->dio_rwsem);
> >> +
> >> if (iov_iter_rw(iter) == WRITE) {
> >> if (err > 0)
> >> set_inode_flag(inode, FI_UPDATE_WRITE);
> >> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >> index bf9a13a..2e439ec 100644
> >> --- a/fs/f2fs/f2fs.h
> >> +++ b/fs/f2fs/f2fs.h
> >> @@ -474,6 +474,7 @@ struct f2fs_inode_info {
> >> struct list_head inmem_pages; /* inmemory pages managed by f2fs */
> >> struct mutex inmem_lock; /* lock for inmemory pages */
> >> struct extent_tree *extent_tree; /* cached extent_tree entry */
> >> + struct rw_semaphore dio_rwsem; /* avoid racing between dio and gc */
> >> };
> >>
> >> static inline void get_extent_info(struct extent_info *ext,
> >> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >> index c612137..a9bfb8d 100644
> >> --- a/fs/f2fs/gc.c
> >> +++ b/fs/f2fs/gc.c
> >> @@ -755,12 +755,25 @@ next_step:
> >> /* phase 3 */
> >> inode = find_gc_inode(gc_list, dni.ino);
> >> if (inode) {
> >> + struct f2fs_inode_info *fi = F2FS_I(inode);
> >> + bool locked = false;
> >> +
> >> + if (S_ISREG(inode->i_mode)) {
> >> + if (!down_write_trylock(&fi->dio_rwsem))
> >> + continue;
> >> + locked = true;
> >> + }
> >> +
> >> start_bidx = start_bidx_of_node(nofs, inode)
> >> + ofs_in_node;
> >> if (f2fs_encrypted_inode(inode) && S_ISREG(inode->i_mode))
> >> move_encrypted_block(inode, start_bidx);
> >> else
> >> move_data_page(inode, start_bidx, gc_type);
> >> +
> >> + if (locked)
> >> + up_write(&fi->dio_rwsem);
> >> +
> >> stat_inc_data_blk_count(sbi, 1, gc_type);
> >> }
> >> }
> >> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> >> index edd1b35..dde57fb 100644
> >> --- a/fs/f2fs/super.c
> >> +++ b/fs/f2fs/super.c
> >> @@ -579,6 +579,7 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb)
> >> INIT_LIST_HEAD(&fi->gdirty_list);
> >> INIT_LIST_HEAD(&fi->inmem_pages);
> >> mutex_init(&fi->inmem_lock);
> >> + init_rwsem(&fi->dio_rwsem);
> >>
> >> /* Will be used by directory only */
> >> fi->i_dir_level = F2FS_SB(sb)->dir_level;
> >> --
> >> 2.7.2
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