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Wed, 20 Jan 2021 22:43:21 -0500 (EST) Received: from mail20.mymailcheap.com (mail20.mymailcheap.com [51.83.111.147]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by filter1.mymailcheap.com (Postfix) with ESMTPS; Wed, 20 Jan 2021 22:43:21 -0500 (EST) Received: from [213.133.102.83] (ml.mymailcheap.com [213.133.102.83]) by mail20.mymailcheap.com (Postfix) with ESMTP id 0E58140AF8; Thu, 21 Jan 2021 03:43:20 +0000 (UTC) Authentication-Results: mail20.mymailcheap.com; dkim=pass (1024-bit key; unprotected) header.d=aosc.io header.i=@aosc.io header.b="O9/n28UZ"; dkim-atps=neutral AI-Spam-Status: Not processed Received: from ice-e5v2.lan (unknown [59.41.163.171]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mail20.mymailcheap.com (Postfix) with ESMTPSA id 7727841EC2; Thu, 21 Jan 2021 03:43:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=aosc.io; s=default; t=1611200594; bh=3+s0yTdz2/e6zrgdoSmiyFqE7ryRDzPPZVDPvSpSv94=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=O9/n28UZCaOdJ4OmatRGyijpVcRjMZ8jU/MiYVGdKGEUYD9/441xbNCc9Ioht7B5a tyYl6eB9eQJ4d3iobxo6orCqzwJgWjXPyma/5/Ant2lJBaiIn1XT1Jhh+0XKEqKD5B SIGG28WCPvANvEPmAQ6adn+LLION7evclUrm2hK0= Message-ID: <83bb613212ee81648e5bf7c0f9cd3219e0046f80.camel@aosc.io> Subject: Re: [PATCH v3] ovl: use a dedicated semaphore for dir upperfile caching From: Icenowy Zheng To: Miklos Szeredi , Amir Goldstein Cc: Xiao Yang , overlayfs , linux-kernel , stable Date: Thu, 21 Jan 2021 11:43:07 +0800 In-Reply-To: <20210120102045.GD1236412@miu.piliscsaba.redhat.com> References: <20210105003611.194511-1-icenowy@aosc.io> <20210120102045.GD1236412@miu.piliscsaba.redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.38.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-0.10 / 10.00]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; R_DKIM_ALLOW(0.00)[aosc.io:s=default]; RECEIVED_SPAMHAUS_PBL(0.00)[59.41.163.171:received]; FROM_HAS_DN(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; DMARC_NA(0.00)[aosc.io]; R_SPF_SOFTFAIL(0.00)[~all]; RCPT_COUNT_FIVE(0.00)[6]; ML_SERVERS(-3.10)[213.133.102.83]; TO_DN_ALL(0.00)[]; DKIM_TRACE(0.00)[aosc.io:+]; FREEMAIL_TO(0.00)[szeredi.hu,gmail.com]; RCVD_NO_TLS_LAST(0.10)[]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:24940, ipnet:213.133.96.0/19, country:DE]; RCVD_COUNT_TWO(0.00)[2]; MID_RHS_MATCH_FROM(0.00)[]; HFILTER_HELO_BAREIP(3.00)[213.133.102.83,1] X-Rspamd-Queue-Id: 0E58140AF8 X-Rspamd-Server: mail20.mymailcheap.com Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org 在 2021-01-20星期三的 11:20 +0100，Miklos Szeredi写道： > On Tue, Jan 05, 2021 at 08:47:41AM +0200, Amir Goldstein wrote: > > On Tue, Jan 5, 2021 at 2:36 AM Icenowy Zheng > > wrote: > > > > > > The function ovl_dir_real_file() currently uses the semaphore of > > > the > > > inode to synchronize write to the upperfile cache field. > > > > Although the inode lock is a rw_sem it is referred to as the "inode > > lock" > > and you also left semaphore in the commit subject. > > No need to re-post. This can be fixed on commit. > > > > > > > > However, this function will get called by ovl_ioctl_set_flags(), > > > which > > > utilizes the inode semaphore too. In this case > > > ovl_dir_real_file() will > > > try to claim a lock that is owned by a function in its call > > > stack, which > > > won't get released before ovl_dir_real_file() returns. > > > > > > Define a dedicated semaphore for the upperfile cache, so that the > > > deadlock won't happen. > > > > > > Fixes: 61536bed2149 ("ovl: support [S|G]ETFLAGS and > > > FS[S|G]ETXATTR ioctls for directories") > > > Cc: stable@vger.kernel.org # v5.10 > > > Signed-off-by: Icenowy Zheng > > > --- > > > Changes in v2: > > > - Fixed missing replacement in error handling path. > > > Changes in v3: > > > - Use mutex instead of semaphore. > > > > > >  fs/overlayfs/readdir.c | 10 +++++----- > > >  1 file changed, 5 insertions(+), 5 deletions(-) > > > > > > diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c > > > index 01620ebae1bd..3980f9982f34 100644 > > > --- a/fs/overlayfs/readdir.c > > > +++ b/fs/overlayfs/readdir.c > > > @@ -56,6 +56,7 @@ struct ovl_dir_file { > > >         struct list_head *cursor; > > >         struct file *realfile; > > >         struct file *upperfile; > > > +       struct mutex upperfile_mutex; > > > > That's a very specific name. > > This mutex protects members of struct ovl_dir_file, which could > > evolve > > into struct ovl_file one day (because no reason to cache only dir > > upper file), > > so I would go with a more generic name, but let's leave it to > > Miklos to decide. > > > > He could have a different idea altogether for fixing this bug. > > How about this (untested) patch? > > It's a cleanup as well as a fix, but maybe we should separate the > cleanup from > the fix... If you are going to post this, feel free to add Tested-by: Icenowy Zheng (And if you remove the IS_ERR(realfile) part, the tested-by tag still applies.) > > Thanks, > Miklos > --- > >  fs/overlayfs/readdir.c |   23 +++++++---------------- >  1 file changed, 7 insertions(+), 16 deletions(-) > > --- a/fs/overlayfs/readdir.c > +++ b/fs/overlayfs/readdir.c > @@ -865,7 +865,7 @@ struct file *ovl_dir_real_file(const str >   >         struct ovl_dir_file *od = file->private_data; >         struct dentry *dentry = file->f_path.dentry; > -       struct file *realfile = od->realfile; > +       struct file *old, *realfile = od->realfile; >   >         if (!OVL_TYPE_UPPER(ovl_path_type(dentry))) >                 return want_upper ? NULL : realfile; > @@ -874,29 +874,20 @@ struct file *ovl_dir_real_file(const str >          * Need to check if we started out being a lower dir, but got > copied up >          */ >         if (!od->is_upper) { > -               struct inode *inode = file_inode(file); > - >                 realfile = READ_ONCE(od->upperfile); >                 if (!realfile) { >                         struct path upperpath; >   >                         ovl_path_upper(dentry, &upperpath); >                         realfile = ovl_dir_open_realfile(file, > &upperpath); > +                       if (IS_ERR(realfile)) > +                               return realfile; >   > -                       inode_lock(inode); > -                       if (!od->upperfile) { > -                               if (IS_ERR(realfile)) { > -                                       inode_unlock(inode); > -                                       return realfile; > -                               } > -                               smp_store_release(&od->upperfile, > realfile); > -                       } else { > -                               /* somebody has beaten us to it */ > -                               if (!IS_ERR(realfile)) > -                                       fput(realfile); > -                               realfile = od->upperfile; > +                       old = cmpxchg_release(&od->upperfile, NULL, > realfile); > +                       if (old) { > +                               fput(realfile); > +                               realfile = old; >                         } > -                       inode_unlock(inode); >                 } >         } >