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    SubjectRe: [BISECTED] 2.6.39rc: kobject-related reboot after RAID array initialization(?) post-QUEUE_FLAG_REENTER-removal
    On Sun, 15 May 2011 23:05:32 +0100 Nix <nix@esperi.org.uk> wrote:

    > After this change:
    >
    > commit c21e6beba8835d09bb80e34961430b13e60381c5
    > Author: Jens Axboe <jaxboe@fusionio.com>
    > Date: Tue Apr 19 13:32:46 2011 +0200
    >
    > block: get rid of QUEUE_FLAG_REENTER
    >
    > We are currently using this flag to check whether it's safe
    > to call into ->request_fn(). If it is set, we punt to kblockd.
    > But we get a lot of false positives and excessive punts to
    > kblockd, which hurts performance.
    >
    > The only real abuser of this infrastructure is SCSI. So export
    > the async queue run and convert SCSI over to use that. There's
    > room for improvement in that SCSI need not always use the async
    > call, but this fixes our performance issue and they can fix that
    > up in due time.
    >
    > Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
    >
    > my system panics and reboots in early userspace. It is slightly
    > difficult to figure out where -- the reboot happens so fast -- but it is
    > either triggered by
    >
    > /sbin/mdadm --assemble --scan --auto=md
    >
    > (with mdadm v2.6.9, yes, I know, it's quite old but it works)
    >
    > or by
    >
    > /sbin/lvm vgscan --ignorelockingfailure --mknodes
    >
    > (most probably the former, since I don't see any sign of lvm running in
    > the text that blinks up right before the reboot, and the oops below
    > mentions md1, not anything lvmish.
    >
    > netconsole reports this (ignore the fact that md1 is resyncing, that's
    > because of previous instances of this bug!):
    >
    > [ 6.773532] md: md0 stopped.
    > [ 6.976368] md: bind<sdb1>
    > [ 6.978284] md: bind<sda1>
    > [ 6.980162] bio: create slab <bio-1> at 1
    > [ 6.981992] md/raid1:md0: active with 2 out of 2 mirrors
    > [ 6.983745] md0: detected capacity change from 0 to 271319040
    > [ 6.987345] md: md1 stopped.
    > [ 6.989411] md0: unknown partition table
    > [ 7.000464] md: bind<sdb3>
    > [ 7.002247] md: bind<sda3>
    > [ 7.003998] md/raid1:md1: not clean -- starting background reconstruction
    > [ 7.005669] md/raid1:md1: active with 2 out of 2 mirrors
    > [ 7.007330] md1: detected capacity change from 0 to 486936436736
    > [ 7.008982] md: resync of RAID array md1
    > [ 7.008984] md: minimum _guaranteed_ speed: 1000 KB/sec/disk.
    > [ 7.008985] md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for resync.
    > [ 7.008988] md: using 128k window, over a total of 475523864 blocks.
    > [ 7.008990] md: resuming resync of md1 from checkpoint.
    > [ 7.176568] md1: unknown partition table
    > [ 7.350823] general protection fault: 0000 [#1] PREEMPT SMP
    > [ 7.353166] last sysfs file: /sys/devices/virtual/block/md1/dev
    > [ 7.355496] CPU 1
    > [ 7.355514] Modules linked in:
    > [ 7.360073]
    > [ 7.362310] Pid: 0, comm: kworker/0:0 Not tainted 2.6.39-rc4-00119-g584f790-dirty #11
    > System manufacturer System Product Name /P6T
    > [ 7.364629] RIP: 0010:[<ffffffff8122bb01>] [<ffffffff8122bb01>] kobject_put+0x11/0x4b
    > [ 7.366921] RSP: 0018:ffff88033fc0e510 EFLAGS: 00010202
    > [ 7.369178] RAX: 0000000400000008 RBX: 3d9e2838ffff8813 RCX: 0000000000000003
    > [ 7.371417] RDX: ffff8803396feec8 RSI: ffff8803391ea800 RDI: 3d9e2838ffff8813
    > [ 7.373621] RBP: ffff88033fc0e520 R08: ffff88033fc0e530 R09: 00000000000003e8
    > [ 7.375827] R10: 0000000001887509 R11: 0000000200000000 R12: ffff8803391ea800
    > [ 7.378040] R13: ffff8803396fee00 R14: ffff88033d9e2848 R15: 0000000000001055
    > [ 7.380265] FS: 0000000000000000(0000) GS:ffff88033fc40000(0000) knlGS:0000000000000000
    > [ 7.382514] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
    > [ 7.384765] CR2: 00000000004051d0 CR3: 000000033a22c000 CR4: 00000000000006e0
    > [ 7.387037] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    > [ 7.389325] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
    > [ 7.391610] Process kworker/0:0 (pid: 0, threadinfo ffff88033e256000, task ffff88033e254300)
    > [ 7.393914] Stack:
    > [ 7.396196] ffff88033fc0e530 ffff88033d9e2800 ffff88033fc0e530 ffffffff81367f19
    > [ 7.398544] ffff88033fc0e580 ffffffff81381614 ffff88033a2669c0 3d9e2838ffff8803
    > [ 7.400876] 0000000000000053 ffff8803396fee00 0000000000000202 0000000000000246
    > [ 7.403207] Call Trace:
    > [ 7.405481] Code: 89 de 48 c7 c7 d8 ee 7d 81 31 c0 e8 c8 7b 33 00 e8
    > 9d 79 33 00 5b 41 5c c9 c3 55 48 89 e5 53 48 89 fb 48 83 ec 08 48 85 ff
    > 74 36 <f6> 47 3c 01 75 20 49 89 f8 48 8b 0f 48 c7 c2 ed ee 7d 81 be 53
    >
    > [ 7.411141] RIP [<ffffffff8122bb01>] kobject_put+0x11/0x4b
    > [ 7.413725] RSP <ffff88033fc0e510>
    > [ 7.416289] ---[ end trace 2a57282106bd5f52 ]---
    > [ 7.418831] Kernel panic - not syncing: Fatal exception in interrupt
    > [ 7.421364] Pid: 0, comm: kworker/0:0 Tainted: G D 2.6.39-rc4-00119-g584f790-dirty #11
    > [ 7.423926] Call Trace:
    >
    > (There is no call trace, ever. I guess it doesn't have time to get over
    > the network before the panic?)

    That is unfortunate....

    I'm having trouble seeing md implicated given the patch, but one never
    knows...

    I'd try reverting just the __blk_run_queue part of the patch.

    i.e. leave __blk_run_queue behaving how it did before the patch, but keep the
    blk_run_queue_async parts of the new code.
    If that still crashes, then there must be someone going wrong when scsi calls
    the new blk_run_queue_async.
    If it doesn't crash, then the recursion-protection of QUEUE_FLAG_REENTER must
    be protecting us from something else other than SCSI re-entering.

    NeilBrown



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