Messages in this thread | | | Date | Wed, 1 Feb 2023 09:40:12 +0800 | Subject | Re: [f2fs-dev] [PATCH] f2fs: synchronize atomic write aborts | From | Chao Yu <> |
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Hi Daeho,
On 2023/2/1 6:34, Daeho Jeong wrote: > On Tue, Jan 31, 2023 at 1:57 PM Daeho Jeong <daeho43@gmail.com> wrote: >> >> On Tue, Jan 31, 2023 at 1:38 PM Daeho Jeong <daeho43@gmail.com> wrote: >>> >>> On Tue, Jan 31, 2023 at 11:13 AM Daeho Jeong <daeho43@gmail.com> wrote: >>>> >>>> Hi Chao, >>>> >>>> On Tue, Jan 31, 2023 at 3:37 AM Chao Yu <chao@kernel.org> wrote: >>>>> >>>>> Hi Daeho, >>>>> >>>>> On 2023/1/31 0:34, Daeho Jeong wrote: >>>>>> Hi Chao, >>>>>> >>>>>> I read your patch series now and I like it. >>>>> >>>>> Thank you for checking the patches. :) >>>>> >>>>>> However, how about a race condition between start_atomic_write and >>>>>> abort_atomic_write? >>>>> >>>>> Yup, I noticed that issue, I guess we can avoid this race condition by >>>>> covering these two flows w/ i_atomic_sem. >>>>> >>>>>> abort_atomic_write is called without inode_lock in closing filp scenarios. >>>>>> What do you think about this? >>>>> >>>>> I'm fine w/ your change as it's more clean, but it's better to drop cow_inode's >>>>> page cache if atomic_write is committed or aborted to avoid caching obsolete page? >>>> >>>> It's better to put that part in f2fs_abort_atomic_write(). >>>> On top of that, maybe, we should move >>>> f2fs_do_truncate_blocks(fi->cow_inode, 0, true) part from >>>> f2fs_ioc_start_atomic_write() to f2fs_abort_atomic_write(), too. >>> >>> Oh, we shouldn't touch the f2fs_do_truncate_blocks() part, since there >>> might be some left writeback after aborting atomic write. >>> Plz. review it related to the timing of calling truncate_inode_pages_final(). >> >> Looks like the scenario becomes too complicated if I think about more >> than one writer's scenario. >> How about we check writecount in commit_atomic_write ioctl and return >> EBUSY when it's not only one writer? >> In that case, we can make the scenario simple and effective, and we >> can release all the resources in abort_atomic_write(). > > Oh, I totally forgot this. We don't use pages of COW inode. So, we
Yes, after atomic_write is committed or aborted, we don't use pages of cow_inode, so they are obsolete, IMO, we'd better to reclaim them immediately to avoid unnecessary memory use.
The implementation may be:
- f2fs_ioc_abort_atomic_write - f2fs_abort_atomic_write - truncate_inode_pages_final(cow_inode)
- f2fs_ioc_commit_atomic_write - f2fs_abort_atomic_write - truncate_inode_pages_final(cow_inode)
Thanks,
> don't need to clean them up. > >> >>> >>>> >>>> Thanks, >>>> >>>>> >>>>> Thanks, >>>>> >>>>>> >>>>>> Thanks, >>>>>> >>>>>> >>>>>> On Fri, Jan 27, 2023 at 6:07 PM Chao Yu <chao@kernel.org> wrote: >>>>>>> >>>>>>> Hi Daeho, Jaegeuk, >>>>>>> >>>>>>> Please take a look at patchset in below link: >>>>>>> >>>>>>> https://lore.kernel.org/linux-f2fs-devel/20230109034453.490176-1-chao@kernel.org/T/#t >>>>>>> >>>>>>> In PATCH 4/5, I'm trying to fix the same issue w/ alternative way, let me >>>>>>> know your preference. :) >>>>>>> >>>>>>> One comment as below. >>>>>>> >>>>>>> On 2023/1/13 8:49, Daeho Jeong wrote: >>>>>>>> From: Daeho Jeong <daehojeong@google.com> >>>>>>>> >>>>>>>> To fix a race condition between atomic write aborts, I use the inode >>>>>>>> lock and make COW inode to be re-usable thoroughout the whole >>>>>>>> atomic file inode lifetime. >>>>>>>> >>>>>>>> Reported-by: syzbot+823000d23b3400619f7c@syzkaller.appspotmail.com >>>>>>>> Fixes: 3db1de0e582c ("f2fs: change the current atomic write way") >>>>>>>> Signed-off-by: Daeho Jeong <daehojeong@google.com> >>>>>>>> --- >>>>>>>> fs/f2fs/file.c | 43 ++++++++++++++++++++++++++++--------------- >>>>>>>> fs/f2fs/inode.c | 11 +++++++++-- >>>>>>>> fs/f2fs/segment.c | 3 --- >>>>>>>> fs/f2fs/super.c | 2 -- >>>>>>>> 4 files changed, 37 insertions(+), 22 deletions(-) >>>>>>>> >>>>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c >>>>>>>> index ecbc8c135b49..ff072a9ed258 100644 >>>>>>>> --- a/fs/f2fs/file.c >>>>>>>> +++ b/fs/f2fs/file.c >>>>>>>> @@ -1866,7 +1866,10 @@ static int f2fs_release_file(struct inode *inode, struct file *filp) >>>>>>>> atomic_read(&inode->i_writecount) != 1) >>>>>>>> return 0; >>>>>>>> >>>>>>>> + inode_lock(inode); >>>>>>>> f2fs_abort_atomic_write(inode, true); >>>>>>>> + inode_unlock(inode); >>>>>>>> + >>>>>>>> return 0; >>>>>>>> } >>>>>>>> >>>>>>>> @@ -1880,8 +1883,11 @@ static int f2fs_file_flush(struct file *file, fl_owner_t id) >>>>>>>> * until all the writers close its file. Since this should be done >>>>>>>> * before dropping file lock, it needs to do in ->flush. >>>>>>>> */ >>>>>>>> - if (F2FS_I(inode)->atomic_write_task == current) >>>>>>>> + if (F2FS_I(inode)->atomic_write_task == current) { >>>>>>>> + inode_lock(inode); >>>>>>>> f2fs_abort_atomic_write(inode, true); >>>>>>>> + inode_unlock(inode); >>>>>>>> + } >>>>>>>> return 0; >>>>>>>> } >>>>>>>> >>>>>>>> @@ -2087,19 +2093,28 @@ static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate) >>>>>>>> goto out; >>>>>>>> } >>>>>>>> >>>>>>>> - /* Create a COW inode for atomic write */ >>>>>>>> - pinode = f2fs_iget(inode->i_sb, fi->i_pino); >>>>>>>> - if (IS_ERR(pinode)) { >>>>>>>> - f2fs_up_write(&fi->i_gc_rwsem[WRITE]); >>>>>>>> - ret = PTR_ERR(pinode); >>>>>>>> - goto out; >>>>>>>> - } >>>>>>>> + /* Check if the inode already has a COW inode */ >>>>>>>> + if (fi->cow_inode == NULL) { >>>>>>>> + /* Create a COW inode for atomic write */ >>>>>>>> + pinode = f2fs_iget(inode->i_sb, fi->i_pino); >>>>>>>> + if (IS_ERR(pinode)) { >>>>>>>> + f2fs_up_write(&fi->i_gc_rwsem[WRITE]); >>>>>>>> + ret = PTR_ERR(pinode); >>>>>>>> + goto out; >>>>>>>> + } >>>>>>>> >>>>>>>> - ret = f2fs_get_tmpfile(mnt_userns, pinode, &fi->cow_inode); >>>>>>>> - iput(pinode); >>>>>>>> - if (ret) { >>>>>>>> - f2fs_up_write(&fi->i_gc_rwsem[WRITE]); >>>>>>>> - goto out; >>>>>>>> + ret = f2fs_get_tmpfile(mnt_userns, pinode, &fi->cow_inode); >>>>>>>> + iput(pinode); >>>>>>>> + if (ret) { >>>>>>>> + f2fs_up_write(&fi->i_gc_rwsem[WRITE]); >>>>>>>> + goto out; >>>>>>>> + } >>>>>>>> + >>>>>>>> + set_inode_flag(fi->cow_inode, FI_COW_FILE); >>>>>>>> + clear_inode_flag(fi->cow_inode, FI_INLINE_DATA); >>>>>>>> + } else { >>>>>>>> + /* Reuse the already created COW inode */ >>>>>>>> + f2fs_do_truncate_blocks(fi->cow_inode, 0, true); >>>>>>>> } >>>>>>>> >>>>>>>> f2fs_write_inode(inode, NULL); >>>>>>>> @@ -2107,8 +2122,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate) >>>>>>>> stat_inc_atomic_inode(inode); >>>>>>>> >>>>>>>> set_inode_flag(inode, FI_ATOMIC_FILE); >>>>>>>> - set_inode_flag(fi->cow_inode, FI_COW_FILE); >>>>>>>> - clear_inode_flag(fi->cow_inode, FI_INLINE_DATA); >>>>>>>> >>>>>>>> isize = i_size_read(inode); >>>>>>>> fi->original_i_size = isize; >>>>>>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c >>>>>>>> index ff6cf66ed46b..4921f7209e28 100644 >>>>>>>> --- a/fs/f2fs/inode.c >>>>>>>> +++ b/fs/f2fs/inode.c >>>>>>>> @@ -766,11 +766,18 @@ int f2fs_write_inode(struct inode *inode, struct writeback_control *wbc) >>>>>>>> void f2fs_evict_inode(struct inode *inode) >>>>>>>> { >>>>>>>> struct f2fs_sb_info *sbi = F2FS_I_SB(inode); >>>>>>>> - nid_t xnid = F2FS_I(inode)->i_xattr_nid; >>>>>>>> + struct f2fs_inode_info *fi = F2FS_I(inode); >>>>>>>> + nid_t xnid = fi->i_xattr_nid; >>>>>>>> int err = 0; >>>>>>>> >>>>>>>> f2fs_abort_atomic_write(inode, true); >>>>>>>> >>>>>>>> + if (fi->cow_inode) { >>>>>>>> + clear_inode_flag(fi->cow_inode, FI_COW_FILE); >>>>>>>> + iput(fi->cow_inode); >>>>>>>> + fi->cow_inode = NULL; >>>>>>>> + } >>>>>>>> + >>>>>>>> trace_f2fs_evict_inode(inode); >>>>>>>> truncate_inode_pages_final(&inode->i_data); >>>>>>>> >>>>>>>> @@ -857,7 +864,7 @@ void f2fs_evict_inode(struct inode *inode) >>>>>>>> stat_dec_inline_inode(inode); >>>>>>>> stat_dec_compr_inode(inode); >>>>>>>> stat_sub_compr_blocks(inode, >>>>>>>> - atomic_read(&F2FS_I(inode)->i_compr_blocks)); >>>>>>>> + atomic_read(&fi->i_compr_blocks)); >>>>>>>> >>>>>>>> if (likely(!f2fs_cp_error(sbi) && >>>>>>>> !is_sbi_flag_set(sbi, SBI_CP_DISABLED))) >>>>>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c >>>>>>>> index ae3c4e5474ef..536d7c674b04 100644 >>>>>>>> --- a/fs/f2fs/segment.c >>>>>>>> +++ b/fs/f2fs/segment.c >>>>>>>> @@ -192,9 +192,6 @@ void f2fs_abort_atomic_write(struct inode *inode, bool clean) >>>>>>>> if (!f2fs_is_atomic_file(inode)) >>>>>>>> return; >>>>>>>> >>>>>>>> - clear_inode_flag(fi->cow_inode, FI_COW_FILE); >>>>>>>> - iput(fi->cow_inode); >>>>>>>> - fi->cow_inode = NULL; >>>>>>>> release_atomic_write_cnt(inode); >>>>>>>> clear_inode_flag(inode, FI_ATOMIC_COMMITTED); >>>>>>>> clear_inode_flag(inode, FI_ATOMIC_REPLACE); >>>>>>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c >>>>>>>> index 1f812b9ce985..10463f084d30 100644 >>>>>>>> --- a/fs/f2fs/super.c >>>>>>>> +++ b/fs/f2fs/super.c >>>>>>>> @@ -1430,8 +1430,6 @@ static int f2fs_drop_inode(struct inode *inode) >>>>>>>> atomic_inc(&inode->i_count); >>>>>>>> spin_unlock(&inode->i_lock); >>>>>>>> >>>>>>>> - f2fs_abort_atomic_write(inode, true); >>>>>>> >>>>>>> In order to avoid caching obsolete page of cow_inode, how about truncating >>>>>>> them here? >>>>>>> >>>>>>> if (f2fs_is_atomic_file() && cow_inode) >>>>>>> truncate_inode_pages_final(&cow_inode->i_data); >>>>>>> >>>>>>> Thanks, >>>>>>> >>>>>>>> - >>>>>>>> /* should remain fi->extent_tree for writepage */ >>>>>>>> f2fs_destroy_extent_node(inode); >>>>>>>>
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