Re: [fuse-devel] [PATCH] fuse: avoid deadlock when write fuse inode

[Huang Jianan]

friendly ping ... 😁

On 2021/2/2 12:11, Huang Jianan via fuse-devel wrote:
> Hi all,
>
>
> This patch works well in our product, but I am not sure this is the 
> correct
>
> way to solve this problem. I think that the inode->i_count shouldn't be
>
> zero after iput is executed in dentry_unlink_inode, then the inode won't
>
> be writeback. But i haven't found where iget is missing.
>
>
> Thanks,
>
> Jianan
>
> On 2021/2/2 12:08, Huang Jianan wrote:
> > We found the following deadlock situations in low memory scenarios:
> > Thread A                         Thread B
> > - __writeback_single_inode
> >   - fuse_write_inode
> >    - fuse_simple_request
> >     - __fuse_request_send
> >      - request_wait_answer
> >                                   - fuse_dev_splice_read
> >                                    - fuse_copy_fill
> >                                     - __alloc_pages_direct_reclaim
> >                                      - do_shrink_slab
> >                                       - super_cache_scan
> >                                        - shrink_dentry_list
> >                                         - dentry_unlink_inode
> >                                          - iput_final
> >                                           - inode_wait_for_writeback
> >
> > The request and inode processed by Thread A and B are the same, which
> > causes a deadlock. To avoid this, we remove the __GFP_FS flag when
> > allocating memory in fuse_copy_fill, so there will be no memory
> > reclaimation in super_cache_scan.
> >
> > Signed-off-by: Huang Jianan <huangjianan@xxxxxxxx>
> > Signed-off-by: Guo Weichao <guoweichao@xxxxxxxx>
> > ---
> >   fs/fuse/dev.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> > index 588f8d1240aa..e580b9d04c25 100644
> > --- a/fs/fuse/dev.c
> > +++ b/fs/fuse/dev.c
> > @@ -721,7 +721,7 @@ static int fuse_copy_fill(struct fuse_copy_state 
> > *cs)
> >               if (cs->nr_segs >= cs->pipe->max_usage)
> >                   return -EIO;
> >   -            page = alloc_page(GFP_HIGHUSER);
> > +            page = alloc_page(GFP_HIGHUSER & ~__GFP_FS);
> >               if (!page)
> >                   return -ENOMEM;