Date: Sat, 25 Oct 2014 17:02:29 +0200 From: Guido Falsi <mad@madpilot.net> To: FreeBSD FS <freebsd-fs@FreeBSD.org> Cc: Glen Barber <gjb@FreeBSD.org>, freebsd-stable@FreeBSD.org Subject: Re: panic: detach with active requests on 10.1-RC3 Message-ID: <544BBB85.2020909@madpilot.net> In-Reply-To: <544A538F.6060202@FreeBSD.org> References: <544A538F.6060202@FreeBSD.org>
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On 10/24/14 15:26, Guido Falsi wrote: > Hi, > > I'm making some experiments with 10.1-RC3 on alix boards as hardware > using NanoBSD. > > By mounting and umounting UFS filesystems I have seen umount constantly > hanging hard in a deadlock. I have tested on two boards with two > distinct compactflash disks with same results. This was not happening > with 10.0-RELEASE. > > I have build a 10.1-RC3 kernel with full debugging and caused the > problem to happen, I got this: > > root@qtest:~ [0]# umount /cfg > panic: detach with active requests > KDB: stack backtrace: > db_trace_self_wrapper(c0968053,c08ea7f0,c2d48800,c23d6bc8,c0536a16,...) > at db_trace_self_wrapper+0x2d/frame 0xc23d6b98 > kdb_backtrace(c09639e1,c09fa7e8,c095761d,c23d6c54,c095761d,...) at > kdb_backtrace+0x30/frame 0xc23d6c00 > vpanic(c09fa682,100,c095761d,c23d6c54,c23d6c54,...) at vpanic+0x80/frame > 0xc23d6c24 > kassert_panic(c095761d,c09575b3,c2d7acc0,4c7,c2d7acc0,...) at > kassert_panic+0xe9/frame 0xc23d6c48 > g_detach(c2d7acc0,4,c095725c,1c2,c09c8d5c,...) at g_detach+0x1d3/frame > 0xc23d6c64 > g_wither_washer(c09f7df4,0,c0956544,124,0,...) at > g_wither_washer+0x109/frame 0xc23d6c90 > g_run_events(0,c23d6d08,c095d42a,3dc,0,...) at g_run_events+0x40/frame > 0xc23d6ccc > fork_exit(c05c4e60,0,c23d6d08) at fork_exit+0x7f/frame 0xc23d6cf4 > fork_trampoline() at fork_trampoline+0x8/frame 0xc23d6cf4 > --- trap 0, eip = 0, esp = 0xc23d6d40, ebp = 0 --- > KDB: enter: panic > [ thread pid 12 tid 100006 ] > Stopped at kdb_enter+0x3d: movl $0,kdb_why > db> > I tried to investigate some more by myself. Maybe what I found is obvious to anyone with decent VFS knowledge, anyway: After some fumbling around I did: db> show geom 0xc2e98b40 consumer: 0xc2e98b40 class: VFS (0xc09c8d5c) geom: ffs.ada0s3 (0xc3293600) provider: ada0s3 (0xc2e7e200) access: r0w0e0 flags: 0x0030 nstart: 19 nend: 18 Which shows nstart != nend, while g_detach asserts them to be the same. Going up the chain of providers I find also it's providers have nstart - nend == 1: db> show geom 0xc2e9b7c0 consumer: 0xc2e9b7c0 class: PART (0xc09c96b0) geom: ada0 (0xc2e7e780) provider: ada0 (0xc2e7e500) access: r2w0e0 flags: 0x0030 nstart: 1430 nend: 1429 db> show geom 0xc2e7e500 provider: ada0 (0xc2e7e500) class: DISK (0xc09c8890) geom: ada0 (0xc2e7e580) mediasize: 4017807360 sectorsize: 512 stripesize: 0 stripeoffset: 0 access: r2w0e0 flags: (0x0030) error: 0 nstart: 2085 nend: 2084 consumer: 0xc2e9a700 (ada0), access=r0w0e0, flags=0x0030 consumer: 0xc2e9b480 (ada0), access=r0w0e0, flags=0x0030 consumer: 0xc2e9b7c0 (ada0), access=r2w0e0, flags=0x0030 Looking at the code these values are touched only in g_io_request() and g_io_deliver() respectively. So this one now looks like a geom problem. In fact the only commit which touched those functions between 10.0 and 10.1 branches is r260385, which merged quite a few things. I've tried reverting it to test without that, but "svn merge -c -260385 ." generated a few conflicts I'm unable to resolve. So I need some guidance even to perform this simple test. > > The machine is sitting there, I am connected with serial console, anyone > willing to help me debug this further? I really know very little about > kernel debugging. If necessary I can also make myself available via IRC > or Jabber. > > It looks like this has some similarities with what was reported here: > > https://lists.freebsd.org/pipermail/freebsd-fs/2014-September/020035.html > > I also tested with head (including r272130) and it does deadlock the same. > After the analysis above I think that there really is no similitude with the probllem reported by bdrewery. -- Guido Falsi <mad@madpilot.net>
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