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Mon, 4 Jan 2021 08:28:27 +0100 (CET) Received: from [213.133.102.83] (ml.mymailcheap.com [213.133.102.83]) by mail20.mymailcheap.com (Postfix) with ESMTP id A9F4F41F21; Mon, 4 Jan 2021 07:28:25 +0000 (UTC) Authentication-Results: mail20.mymailcheap.com; dkim=pass (1024-bit key; unprotected) header.d=aosc.io header.i=@aosc.io header.b="hA4RwVr+"; dkim-atps=neutral AI-Spam-Status: Not processed Received: from ICE-E5V2.lan (unknown [59.41.162.25]) (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 25C6041F21; Mon, 4 Jan 2021 07:28:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=aosc.io; s=default; t=1609745299; bh=fjnZkoVTTU0sciv5VPvHtJlIseKPWNwKRM7jiM31Sc8=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=hA4RwVr+3RnYQfmb1U0QtTJJbQue5JHkytRUS8NkFeOBbK3yZYGF7J+iUm//UOBTA FJ9+p1w9rJAh00VwgbSwUBGbfLAvx+1OYqFYhMMlBiiDaWxmCpVYVU3Ceb235EDrcw FFtahrrANP94o83vM08EcDpxlmC+ceJaUed3j3fU= Message-ID: Subject: Re: [PATCH] ovl: use a dedicated semaphore for dir upperfile caching From: Icenowy Zheng To: Amir Goldstein Cc: Miklos Szeredi , Xiao Yang , overlayfs , linux-kernel , stable Date: Mon, 04 Jan 2021 15:28:12 +0800 In-Reply-To: References: <20210101201230.768653-1-icenowy@aosc.io> 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)[59.41.162.25: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)[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: A9F4F41F21 X-Rspamd-Server: mail20.mymailcheap.com Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org 在 2021-01-03星期日的 16:10 +0200，Amir Goldstein写道： > On Fri, Jan 1, 2021 at 10:12 PM Icenowy Zheng > wrote: > > > > The function ovl_dir_real_file() currently uses the semaphore of > > the > > inode to synchronize write to the upperfile cache field. > > > > 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. > > oops. I wondered why I didn't see any warnings on this from lockdep. > Ah! because the xfstest that exercises ovl_ioctl_set_flags() on > directory, > generic/079, starts with an already upper dir. > > And the xfstest that checks chattr+i on lower/upper files, > overlay/040, > does not check chattr on dirs (ioctl on overlay dirs wasn't supported > at > the time the test was written). > > Would you be able to create a variant of test overlay/040 that also > tests > chattr +i on lower/upper dirs to test your patch and confirm that the > test > fails on master with the appropriate Kconfig debug options. https://gist.github.com/Icenowy/c7d8decb6812d6e5064d143c57281ad3 Here's a test that would break on master (I used linux-next/master for test). [ 246.521880] INFO: task chattr:715 blocked for more than 122 seconds. [ 246.525659] Not tainted 5.11.0-rc1-next-20210104+ #20 [ 246.528498] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 246.535076] task:chattr state:D stack:13736 pid: 715 ppid: 529 flags:0x00000000 [ 246.538923] Call Trace: [ 246.540241] __schedule+0x2a9/0x820 [ 246.541986] schedule+0x56/0xc0 [ 246.543616] rwsem_down_write_slowpath+0x375/0x630 [ 246.545565] ovl_dir_real_file+0xc1/0x120 [ 246.547512] ovl_real_fdget+0x35/0x80 [ 246.549303] ovl_real_ioctl+0x26/0x90 [ 246.551050] ? mnt_drop_write+0x2c/0x70 [ 246.553068] ovl_ioctl_set_flags+0x93/0x110 [ 246.555407] __x64_sys_ioctl+0x7e/0xb0 [ 246.557175] do_syscall_64+0x33/0x40 [ 246.558869] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 246.561057] RIP: 0033:0x7fe4a3830b67 [ 246.565799] RSP: 002b:00007ffe7ad504f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 246.569438] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fe4a3830b67 [ 246.572061] RDX: 00007ffe7ad5050c RSI: 0000000040086602 RDI: 0000000000000003 [ 246.575509] RBP: 0000000000000003 R08: 0000000000000001 R09: 0000000000000000 [ 246.578932] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000010 [ 246.581014] R13: 00007ffe7ad50810 R14: 0000000000000002 R15: 0000000000000001 [ 246.582818] [ 246.582818] Showing all locks held in the system: [ 246.584741] 1 lock held by khungtaskd/18: [ 246.586085] #0: ffffffff9e951540 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x15/0x100 [ 246.589775] 3 locks held by chattr/715: [ 246.591364] #0: ffff96a74b92c450 (sb_writers#11){....}-{0:0}, at: ovl_ioctl_set_flags+0x2f/0x110 [ 246.597182] #1: ffff96a7489c3500 (&ovl_i_mutex_dir_key[depth]){....}-{3:3}, at: ovl_ioctl_set_flags+0x54/0x110 [ 246.601325] #2: ffff96a7489c3500 (&ovl_i_mutex_dir_key[depth]){....}-{3:3}, at: ovl_dir_real_file+0xc1/0x120 > > > > > 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 > > --- > >  fs/overlayfs/readdir.c | 6 ++++-- > >  1 file changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c > > index 01620ebae1bd..f10701aabb71 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 semaphore upperfile_sem; > > mutex please > > >  }; > > > >  static struct ovl_cache_entry *ovl_cache_entry_from_node(struct > > rb_node *n) > > @@ -883,7 +884,7 @@ struct file *ovl_dir_real_file(const struct > > file *file, bool want_upper) > >                         ovl_path_upper(dentry, &upperpath); > >                         realfile = ovl_dir_open_realfile(file, > > &upperpath); > > > > -                       inode_lock(inode); > > +                       down(&od->upperfile_sem); > >                         if (!od->upperfile) { > >                                 if (IS_ERR(realfile)) { > >                                         inode_unlock(inode); > > You missed this unlock Thanks, will send v2 now. > > Thanks, > Amir.