lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <CAFLxGvxySJ9WvNTOjww9OG5KB-q++72WT3QcrCGAFW1M=C9DhA@mail.gmail.com> Date: Tue, 16 Sep 2014 18:50:19 +0200 From: Richard Weinberger <richard.weinberger@...il.com> To: Richard Weinberger <richard@....at> Cc: Thorsten Knabe <linux@...rsten-knabe.de>, LKML <linux-kernel@...r.kernel.org>, Thomas Meyer <thomas@...3r.de>, Valdis Kletnieks <Valdis.Kletnieks@...edu> Subject: Re: [PATCH] UML: UBD: Fix for processes stuck in D state forever in UserModeLinux On Mon, Aug 25, 2014 at 4:04 PM, Richard Weinberger <richard@....at> wrote: > Am 25.08.2014 16:00, schrieb Thorsten Knabe: >> On 08/25/2014 03:25 PM, Richard Weinberger wrote: >>> Am 25.08.2014 01:02, schrieb Thorsten Knabe: >>>> On 08/24/2014 02:11 PM, Richard Weinberger wrote: >>>>> Am 23.08.2014 19:43, schrieb Thorsten Knabe: >>>>>> Hi Richard. >>>>>> >>>>>> On 08/23/2014 05:34 PM, Richard Weinberger wrote: >>>>>>> Hi! >>>>>>> >>>>>>> Am 23.08.2014 15:47, schrieb Thorsten Knabe: >>>>>>>> From: Thorsten Knabe <linux@...rsten-knabe.de> >>>>>>>> >>>>>>>> UML: UBD: Fix for processes stuck in D state forever in UserModeLinux. >>>>>>>> >>>>>>>> Starting with Linux 3.12 processes get stuck in D state forever in >>>>>>>> UserModeLinux under sync heavy workloads. This bug was introduced by >>>>>>>> commit 805f11a0d5 (um: ubd: Add REQ_FLUSH suppport). >>>>>>>> Fix bug by adding a check if FLUSH request was successfully submitted to >>>>>>>> the I/O thread and keeping the FLUSH request on the request queue on >>>>>>>> submission failures. >>>>>>>> >>>>>>>> Fixes: 805f11a0d5 (um: ubd: Add REQ_FLUSH suppport) >>>>>>>> Signed-off-by: Thorsten Knabe <linux@...rsten-knabe.de> >>>>>>> >>>>>>> Thanks a lot for hunting this issue down. >>>>>>> >>>>>>>> --- >>>>>>>> Patch applies to 3.16.1. >>>>>>>> >>>>>>>> diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c >>>>>>>> index 3716e69..b7d2840 100644 >>>>>>>> --- a/arch/um/drivers/ubd_kern.c >>>>>>>> +++ b/arch/um/drivers/ubd_kern.c >>>>>>>> @@ -1277,7 +1277,7 @@ static void do_ubd_request(struct request_queue *q) >>>>>>>> >>>>>>>> while(1){ >>>>>>>> struct ubd *dev = q->queuedata; >>>>>>>> - if(dev->end_sg == 0){ >>>>>>>> + if(dev->request == NULL){ >>>>>>> >>>>>>> Why do we need this specific change? >>>>>> >>>>>> This change is required, because for FLUSH requests dev->end_sg is >>>>>> initialized to 0 by blk_rq_map_sg() a few lines above, as FLUSH requests >>>>>> have no data blocks attached to themselves. >>>>> >>>>> You meant "below"? Looks like I really miss something here. >>>>> At the bottom of the while(1) loop we have >>>>> dev->end_sg = 0; >>>>> dev->request = NULL; >>>> >>>> No. The problematic line is: >>>> dev->end_sg = blk_rq_map_sg(q, req, dev->sg); >>>> and blk_rq_map_sg() returning 0 for REQ_FLUSH requests, because they >>>> have no associated data blocks. >>>> >>>> Hence on the next iteration of the while(1) loop: >>>> if(dev->end_sg == 0){ >>> >>> At the bottom of the while loop dev->end_sg will be set to 0 anyway, this is what puzzles >>> me so hard. >>> (And dev->request too) >> >> Yes, but the statements: >> dev->end_sg = 0; >> dev->request = NULL; >> at the end of the while loop will only be reached (for FLUSH requests >> only with my patch applied) when submit_request() succeeds. Otherwise >> the function do_ubd_request() returns early leaving dev->end_sg and >> dev->request untouched. > > Can you please add this info into the commit message, I'm sure others get also > confused by that.^^ > The logic in do_ubd_request() royal mess which needs fixing too. :-\ Hmm, you didn't resend the patch. I'll amend the commit message myself and push it to Linus this week. -- Thanks, //richard -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists