Messages in this thread | | | Subject | Re: [PATCH] f2fs: Fix deadlock under storage almost full/dirty condition | From | Chao Yu <> | Date | Mon, 11 Nov 2019 15:18:14 +0800 |
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Hi Sahitya,
On 2019/11/11 14:44, Sahitya Tummala wrote: > Hi Chao, > > On Mon, Nov 11, 2019 at 02:28:47PM +0800, Chao Yu wrote: >> Hi Sahitya, >> >> On 2019/11/11 11:40, Sahitya Tummala wrote: >>> Hi Chao, >>> >>> On Mon, Nov 11, 2019 at 10:51:10AM +0800, Chao Yu wrote: >>>> On 2019/11/8 19:03, Sahitya Tummala wrote: >>>>> There could be a potential deadlock when the storage capacity >>>>> is almost full and theren't enough free segments available, due >>>>> to which FG_GC is needed in the atomic commit ioctl as shown in >>>>> the below callstack - >>>>> >>>>> schedule_timeout >>>>> io_schedule_timeout >>>>> congestion_wait >>>>> f2fs_drop_inmem_pages_all >>>>> f2fs_gc >>>>> f2fs_balance_fs >>>>> __write_node_page >>>>> f2fs_fsync_node_pages >>>>> f2fs_do_sync_file >>>>> f2fs_ioctl >>>>> >>>>> If this inode doesn't have i_gc_failures[GC_FAILURE_ATOMIC] set, >>>>> then it waits forever in f2fs_drop_inmem_pages_all(), for this >>>>> atomic inode to be dropped. And the rest of the system is stuck >>>>> waiting for sbi->gc_mutex lock, which is acquired by f2fs_balance_fs() >>>>> in the stack above. >>>> >>>> I think the root cause of this issue is there is potential infinite loop in >>>> f2fs_drop_inmem_pages_all() for the case of gc_failure is true, because once the >>>> first inode in inode_list[ATOMIC_FILE] list didn't suffer gc failure, we will >>>> skip dropping its in-memory cache and calling iput(), and traverse the list >>>> again, most possibly there is the same inode in the head of that list. >>>> >>> >>> I thought we are expecting for those atomic updates (without any gc failures) to be >>> committed by doing congestion_wait() and thus retrying again. Hence, I just >> >> Nope, we only need to drop inode which encounter gc failures, and keep the rest >> inodes. >> >>> fixed only if we are ending up waiting for commit to happen in the atomic >>> commit path itself, which will be a deadlock. >> >> Look into call stack you provide, I don't think it's correct to drop such inode, >> as its dirty pages should be committed before f2fs_fsync_node_pages(), so >> calling f2fs_drop_inmem_pages won't release any inmem pages, and won't help >> looped GC caused by skipping due to inmem pages. >> >> And then I figure out below fix... >> > > Thanks for the explanation. > The fix below looks good to me.
So could you submit v2? :)
Thanks,
> > Thanks, > Sahitya. > >>> >>>> Could you please check below fix: >>>> >>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h >>>> index 7bf7b0194944..8a3a35b42a37 100644 >>>> --- a/fs/f2fs/f2fs.h >>>> +++ b/fs/f2fs/f2fs.h >>>> @@ -1395,6 +1395,7 @@ struct f2fs_sb_info { >>>> unsigned int gc_mode; /* current GC state */ >>>> unsigned int next_victim_seg[2]; /* next segment in victim section */ >>>> /* for skip statistic */ >>>> + unsigned int atomic_files; /* # of opened atomic file */ >>>> unsigned long long skipped_atomic_files[2]; /* FG_GC and BG_GC */ >>>> unsigned long long skipped_gc_rwsem; /* FG_GC only */ >>>> >>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c >>>> index ecd063239642..79f4b348951a 100644 >>>> --- a/fs/f2fs/file.c >>>> +++ b/fs/f2fs/file.c >>>> @@ -2047,6 +2047,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp) >>>> spin_lock(&sbi->inode_lock[ATOMIC_FILE]); >>>> if (list_empty(&fi->inmem_ilist)) >>>> list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]); >>>> + sbi->atomic_files++; >>>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]); >>>> >>>> /* add inode in inmem_list first and set atomic_file */ >>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c >>>> index 8b977bbd6822..6aa0bb693697 100644 >>>> --- a/fs/f2fs/segment.c >>>> +++ b/fs/f2fs/segment.c >>>> @@ -288,6 +288,8 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi, >>>> bool gc_failure) >>>> struct list_head *head = &sbi->inode_list[ATOMIC_FILE]; >>>> struct inode *inode; >>>> struct f2fs_inode_info *fi; >>>> + unsigned int count = sbi->atomic_files; >>> >>> If the sbi->atomic_files decrements just after this, then the below exit condition >>> may not work. In that case, looped will never be >= count. >>> >>>> + unsigned int looped = 0; >>>> next: >>>> spin_lock(&sbi->inode_lock[ATOMIC_FILE]); >>>> if (list_empty(head)) { >>>> @@ -296,22 +298,29 @@ void f2fs_drop_inmem_pages_all(struct f2fs_sb_info *sbi, >>>> bool gc_failure) >>>> } >>>> fi = list_first_entry(head, struct f2fs_inode_info, inmem_ilist); >>>> inode = igrab(&fi->vfs_inode); >>>> + if (inode) >>>> + list_move_tail(&fi->inmem_ilist, head); >>>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]); >>>> >>>> if (inode) { >>>> if (gc_failure) { >>>> - if (fi->i_gc_failures[GC_FAILURE_ATOMIC]) >>>> - goto drop; >>>> - goto skip; >>>> + if (!fi->i_gc_failures[GC_FAILURE_ATOMIC]) >>>> + goto skip; >>>> } >>>> -drop: >>>> set_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST); >>>> f2fs_drop_inmem_pages(inode); >>>> +skip: >>>> iput(inode); >>> >>> Does this result into f2fs_evict_inode() in this context for this inode? >> >> Yup, we need to call igrab/iput in pair in f2fs_drop_inmem_pages_all() anyway. >> >> Previously, we may have .i_count leak... >> >> Thanks, >> >>> >>> thanks, >>> >>>> } >>>> -skip: >>>> + >>>> congestion_wait(BLK_RW_ASYNC, HZ/50); >>>> cond_resched(); >>>> + >>>> + if (gc_failure) { >>>> + if (++looped >= count) >>>> + return; >>>> + } >>>> + >>>> goto next; >>>> } >>>> >>>> @@ -334,6 +343,7 @@ void f2fs_drop_inmem_pages(struct inode *inode) >>>> spin_lock(&sbi->inode_lock[ATOMIC_FILE]); >>>> if (!list_empty(&fi->inmem_ilist)) >>>> list_del_init(&fi->inmem_ilist); >>>> + sbi->atomic_files--; >>>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]); >>>> } >>>> >>>> Thanks, >>> >
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