Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 4 Jul 2022 03:10:17 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Xiubo Li <xiubli@redhat.com>
Cc:     Jeff Layton <jlayton@kernel.org>, idryomov@gmail.com,
        dhowells@redhat.com, vshankar@redhat.com,
        linux-kernel@vger.kernel.org, ceph-devel@vger.kernel.org,
        keescook@chromium.org, linux-fsdevel@vger.kernel.org,
        linux-cachefs@redhat.com
Subject: Re: [PATCH 1/2] netfs: release the folio lock and put the folio
 before retrying
Message-ID: <YsJMCZB/ecQQha+/@casper.infradead.org>
References: <20220701022947.10716-1-xiubli@redhat.com>
 <20220701022947.10716-2-xiubli@redhat.com>
 <30a4bd0e19626f5fb30f19f0ae70fba2debb361a.camel@kernel.org>
 <f55d10f8-55f6-f56c-bb41-bce139869c8d@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <f55d10f8-55f6-f56c-bb41-bce139869c8d@redhat.com>
Precedence: bulk

On Mon, Jul 04, 2022 at 09:13:44AM +0800, Xiubo Li wrote:
> On 7/1/22 6:38 PM, Jeff Layton wrote:
> > I don't know here... I think it might be better to just expect that when
> > this function returns an error that the folio has already been unlocked.
> > Doing it this way will mean that you will lock and unlock the folio a
> > second time for no reason.
> > 
> > Maybe something like this instead?
> > 
> > diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
> > index 42f892c5712e..8ae7b0f4c909 100644
> > --- a/fs/netfs/buffered_read.c
> > +++ b/fs/netfs/buffered_read.c
> > @@ -353,7 +353,7 @@ int netfs_write_begin(struct netfs_inode *ctx,
> >                          trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
> >                          if (ret == -EAGAIN)
> >                                  goto retry;
> > -                       goto error;
> > +                       goto error_unlocked;
> >                  }
> >          }
> > @@ -418,6 +418,7 @@ int netfs_write_begin(struct netfs_inode *ctx,
> >   error:
> >          folio_unlock(folio);
> >          folio_put(folio);
> > +error_unlocked:
> >          _leave(" = %d", ret);
> >          return ret;
> >   }
> 
> Then the "afs" won't work correctly:
> 
> 377 static int afs_check_write_begin(struct file *file, loff_t pos, unsigned
> len,
> 378????????????????????????????????? struct folio *folio, void **_fsdata)
> 379 {
> 380???????? struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
> 381
> 382???????? return test_bit(AFS_VNODE_DELETED, &vnode->flags) ? -ESTALE : 0;
> 383 }
> 
> The "afs" does nothing with the folio lock.

It's OK to fix AFS too.