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. 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, > > -- -- Sent by a consultant of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel