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Date: Tue, 12 Jul 2016 09:28:26 +0800
From: Chao Yu <yuchao0@...wei.com>
To: Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>
CC: <linux-f2fs-devel@...ts.sourceforge.net>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] f2fs: fix to avoid data update racing between GC and
DIO
On 2016/7/10 0:22, Jaegeuk Kim wrote:
> 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?
If we reuse inode->i_rwsem here, we will suffer the same issue when we remove
i_rwsem lock in dio writer or dio reader for better concurrency.
So I think it's better to use separate lock to just fix this issue.
Thanks,
>
>>
>> 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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