From mboxrd@z Thu Jan 1 00:00:00 1970 From: vaughan Subject: Re: [PATCH v5 0/4] [SCSI] sg: fix race condition in sg_open Date: Mon, 05 Aug 2013 10:19:44 +0800 Message-ID: <51FF0BC0.5020702@oracle.com> References: <1374075246-22923-1-git-send-email-vaughan.cao@oracle.com> <1374468033-8947-1-git-send-email-vaughan.cao@oracle.com> <20130722170338.GA15824@logfs.org> <51F9EB97.7070305@interlog.com> <51FC9449.4060906@interlog.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <51FC9449.4060906@interlog.com> Sender: linux-kernel-owner@vger.kernel.org To: dgilbert@interlog.com Cc: =?UTF-8?B?SsO2cm4gRW5nZWw=?= , JBottomley@parallels.com, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-scsi@vger.kernel.org On 08/03/2013 01:25 PM, Douglas Gilbert wrote: > On 13-08-01 01:01 AM, Douglas Gilbert wrote: >> On 13-07-22 01:03 PM, J=C3=B6rn Engel wrote: >>> On Mon, 22 July 2013 12:40:29 +0800, Vaughan Cao wrote: >>>> >>>> There is a race when open sg with O_EXCL flag. Also a race may >>>> happen between >>>> sg_open and sg_remove. >>>> >>>> Changes from v4: >>>> * [3/4] use ERR_PTR series instead of adding another parameter i= n >>>> sg_add_sfp >>>> * [4/4] fix conflict for cherry-pick from v3. >>>> >>>> Changes from v3: >>>> * release o_sem in sg_release(), not in sg_remove_sfp(). >>>> * not set exclude with sfd_lock held. >>>> >>>> Vaughan Cao (4): >>>> [SCSI] sg: use rwsem to solve race during exclusive open >>>> [SCSI] sg: no need sg_open_exclusive_lock >>>> [SCSI] sg: checking sdp->detached isn't protected when open >>>> [SCSI] sg: push file descriptor list locking down to per-device >>>> locking >>>> >>>> drivers/scsi/sg.c | 178 >>>> +++++++++++++++++++++++++----------------------------- >>>> 1 file changed, 83 insertions(+), 95 deletions(-) >>> >>> Patchset looks good to me, although I didn't test it on hardware ye= t. >>> Signed-off-by: Joern Engel >>> >>> James, care to pick this up? >> >> Acked-by: Douglas Gilbert >> >> Tested O_EXCL with multiple processes and threads; passed. >> sg driver prior to this patch had "leaky" O_EXCL logic >> according to the same test. Block device passed. >> >> James, could you clean this up: >> drivers/scsi/sg.c:242:6: warning: unused variable =E2=80=98res=E2= =80=99 >> [-Wunused-variable] > > Further testing suggests this patch on the sg driver is > broken, so I'll rescind my ack. > > The case it is broken for is when a device is opened > without O_EXCL. Now if, while it is open, a second > thread/process tries to open the same device O_EXCL > then IMO the second open should fail with EBUSY. > > My testing shows that O_EXCL opens properly deflect > other O_EXCL opens. Hi Doug, My test don't have this issue. The routine is something as below: I start three opens without O_EXCL, wait 30s each, and open with O_EXCL|O_NONBLOCK, it failed with EBUSY. And I also call myopen with/without O_EXCL many times in background at the same time, and the test is passed. I don't know why it failed in your test. Usage: myopen [-e][-n][-d delay] -f file -e: exclude -n: nonblock -d: delay N seconds and then close. [root@vacaowol5 16835013]# ./myopen -f /dev/sg5 -d 30 & [1] 3417 [root@vacaowol5 16835013]# ./myopen -f /dev/sg5 -d 30 & [2] 3418 [root@vacaowol5 16835013]# ./myopen -f /dev/sg5 -d 30 & [3] 3419 [root@vacaowol5 16835013]# cat /proc/scsi/sg/debug max_active_device=3D6(origin 1) def_reserved_size=3D32768 >>> device=3Dsg5 scsi5 chan=3D0 id=3D1 lun=3D0 em=3D0 sg_tablesize=3D= 55 excl=3D0 FD(1): timeout=3D60000ms bufflen=3D32768 (res)sgat=3D1 low_dma=3D0 cmd_q=3D0 f_packid=3D0 k_orphan=3D0 closed=3D0 No requests active FD(2): timeout=3D60000ms bufflen=3D32768 (res)sgat=3D1 low_dma=3D0 cmd_q=3D0 f_packid=3D0 k_orphan=3D0 closed=3D0 No requests active FD(3): timeout=3D60000ms bufflen=3D32768 (res)sgat=3D1 low_dma=3D0 cmd_q=3D0 f_packid=3D0 k_orphan=3D0 closed=3D0 No requests active [root@vacaowol5 16835013]# ./myopen -e -n -f /dev/sg5 -d 30 & [4] 3422 [3422:3351] /dev/sg5:exclude: Device or resource busy [4]+ Exit 1 ./myopen -e -n -f /dev/sg5 -d 30 [root@vacaowol5 16835013]# cat /proc/scsi/sg/debug max_active_device=3D6(origin 1) def_reserved_size=3D32768 >>> device=3Dsg5 scsi5 chan=3D0 id=3D1 lun=3D0 em=3D0 sg_tablesize=3D= 55 excl=3D0 FD(1): timeout=3D60000ms bufflen=3D32768 (res)sgat=3D1 low_dma=3D0 cmd_q=3D0 f_packid=3D0 k_orphan=3D0 closed=3D0 No requests active FD(2): timeout=3D60000ms bufflen=3D32768 (res)sgat=3D1 low_dma=3D0 cmd_q=3D0 f_packid=3D0 k_orphan=3D0 closed=3D0 No requests active FD(3): timeout=3D60000ms bufflen=3D32768 (res)sgat=3D1 low_dma=3D0 cmd_q=3D0 f_packid=3D0 k_orphan=3D0 closed=3D0 No requests active [root@vacaowol5 16835013]# cat /proc/scsi/sg/debug [1] Done ./myopen -f /dev/sg5 -d 30 [2]- Done ./myopen -f /dev/sg5 -d 30 [3]+ Done ./myopen -f /dev/sg5 -d 30 > > BTW the standard block driver (e.g. /dev/sdc) is broken > in exactly the same way, according to my tests. > > Doug Gilbert > >