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
fixed only if we are ending up waiting for commit to happen in the atomic
commit path itself, which will be a deadlock.
> 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?
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.
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