Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753440Ab3H0NPT (ORCPT ); Tue, 27 Aug 2013 09:15:19 -0400 Received: from smtp.infotech.no ([82.134.31.41]:53348 "EHLO smtp.infotech.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752414Ab3H0NPR (ORCPT ); Tue, 27 Aug 2013 09:15:17 -0400 Message-ID: <521CA60E.2040802@interlog.com> Date: Tue, 27 Aug 2013 15:13:50 +0200 From: Douglas Gilbert Reply-To: dgilbert@interlog.com User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130803 Thunderbird/17.0.8 MIME-Version: 1.0 To: vaughan CC: =?UTF-8?B?SsO2cm4gRW5nZWw=?= , JBottomley@parallels.com, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 0/4] [SCSI] sg: fix race condition in sg_open 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> <51FF0BC0.5020702@oracle.com> <5200108A.9020008@interlog.com> <52099E1B.5000203@oracle.com> <5209A50E.8090300@interlog.com> <521C606C.3000109@oracle.com> In-Reply-To: <521C606C.3000109@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9188 Lines: 223 On 13-08-27 10:16 AM, vaughan wrote: > On 08/13/2013 11:16 AM, Douglas Gilbert wrote: >> On 13-08-12 10:46 PM, vaughan wrote: >>> On 08/06/2013 04:52 AM, Douglas Gilbert wrote: >>>> On 13-08-04 10:19 PM, vaughan wrote: >>>>> 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, Jörn 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 in >>>>>>>>> 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 >>>>>>>> yet. >>>>>>>> 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 ‘res’ >>>>>>> [-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=6(origin 1) >>>>> def_reserved_size=32768 >>>>> >>> device=sg5 scsi5 chan=0 id=1 lun=0 em=0 sg_tablesize=55 >>>>> excl=0 >>>>> FD(1): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0 >>>>> cmd_q=0 f_packid=0 k_orphan=0 closed=0 >>>>> No requests active >>>>> FD(2): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0 >>>>> cmd_q=0 f_packid=0 k_orphan=0 closed=0 >>>>> No requests active >>>>> FD(3): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0 >>>>> cmd_q=0 f_packid=0 k_orphan=0 closed=0 >>>>> 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=6(origin 1) >>>>> def_reserved_size=32768 >>>>> >>> device=sg5 scsi5 chan=0 id=1 lun=0 em=0 sg_tablesize=55 >>>>> excl=0 >>>>> FD(1): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0 >>>>> cmd_q=0 f_packid=0 k_orphan=0 closed=0 >>>>> No requests active >>>>> FD(2): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0 >>>>> cmd_q=0 f_packid=0 k_orphan=0 closed=0 >>>>> No requests active >>>>> FD(3): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0 >>>>> cmd_q=0 f_packid=0 k_orphan=0 closed=0 >>>>> 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 >>>>> >>>> >>>> Hi, >>>> After the initial failures about 36 hours ago, retesting >>>> yesterday and today has not produced any unexpected >>>> failures. And I have been trying hard on lk 3.10.4 and >>>> lk 3.10.5 . >>>> >>>> My test program is a bit more intense than yours and can >>>> be found in the sg3_utils beta in the News section of this >>>> page: >>>> http://sg.danny.cz/sg/ >>>> >>>> It is in the examples directory, two variants called >>>> sg_tst_excl and sg_tst_excl2 . You will need a recent gcc >>>> compiler, IOW something that can compile c++11 . gcc 4.7.3 >>>> in Ubuntu 13.04 only just manages, fedora 19 should do >>>> better with gcc 4.8.1 . The threading is implemented using >>>> pthreads so it should be reliable. >>>> >>>> Typically I run multiple instances (processes) and each has >>>> multiple threads. One instance can run '-x' which will cause >>>> its first thread not to use O_EXCL **. All my tests currently >>>> use O_NONBLOCK and that leads to lots of EBUSYs (sometimes >>>> in the billions). >>>> >>>> Doug Gilbert >>>> >>>> >>>> ** Using '-x' on two instances will cause an expected failure >>>> so can be used as a control. >>>> >>> Hi Doug, >>> >>> Can I regard this as you ACK it again? >> >> Hi, >> I'd like you to test your setup with sg_tst_excl or sg_tst_excl2 . >> Since my last email, I have not seen any more failures with those >> tests on the patched sg driver but I did see a couple on >> /dev/sd* . With sg_tst_excl2, bsg devices can be used and since bsg >> accepts and ignores O_EXCL, it fails reliably. >> >> BTW I use scsi_debug with 'delay=0' for a pseudo device. >> >> Doug Gilbert > Hi Doug, > > I run test for sg and sd drivers with both sg_tst_excl and sg_tst_excl2 > on kernel vanilla 3.10.9 with mypatches included on Fedora19 x86_64 > baremachine. > * I've tried several times with different -w and -n setting, no failure > for sg driver found. > * It's easy to find failure on both patched and non-patched kernel for > sd driver with the following test command: > ./sg_tst_excl -w 3 -n 2000 -t 16 -x $1 & > ./sg_tst_excl -w 3 -n 2000 -t 16 $1 & > ./sg_tst_excl -w 0 -n 2000 -t 16 $1 & > ./sg_tst_excl -w -1 -n 2000 -t 16 $1 & > ./sg_tst_excl -w -2 -n 2000 -t 16 $1 & > I think option '-w 0/-1/-2' is significant to trigger the failure, since > when I only use '-w >0', test usually passed. Hi, Thanks for testing that. For others trying to follow this, the usage message for that test utility is: Usage: sg_tst_excl [-b] [-l ] [-n ] [-t ] [-V] [-w ] [-x] where -b block on open (def: O_NONBLOCK) -l logical block to increment (def: 1000) -n number of loops per thread (def: 200) -t number of threads (def: 4) -V print version number then exit -w >0: sleep_for(); =0: yield(); -1: no wait; -2: sleep(0) (def: 0) -x don't use O_EXCL on first thread (def: use O_EXCL on all threads) Test O_EXCL open flag with sg driver. Each open/close cycle with the O_EXCL flag does a double increment on lba (using its first 4 bytes). ---------------------- The test is using O_EXCL as a lock so that if a 4 byte integer in a block starts out as even (and for a scsi_debug pseudo, blocks are zero filled) then a open,double_increment,close sequence should always see an even number after the open. Notice that it should be safe for one process to run with '-x' so that its first thread opens the device without the O_EXCL flag. Acked-by: Douglas Gilbert And I let you run with the sd driver quirk :-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/