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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sun, 5 Feb 2012 14:55:47 -0800
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Subject: Re: [BUG 3.3-rc2] spinlock trylock failure on UP on CPU#0
To: Knut Petersen <Knut_Petersen@t-online.de>, Jens Axboe <axboe@kernel.dk>,
        Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org
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Ok, interesting. You're triggering the issue because you have a UP
build with the spinlock debugging code enabled.

On Sun, Feb 5, 2012 at 12:57 PM, Knut Petersen
<Knut_Petersen@t-online.de> wrote:
> Booting ?23783f817bceedd6d4e549385e3f400ea64059e5 I get the following trace
> an AOpen i915GMm-hfs with Pentium-M Dothan:

This is probably the same "technically legal" code that LOCKDEP also
is unhappy about - the nested fast path release. We do a trylock on
the queue lock while we already are holding the queue lock
recursively.

Jens, Tejun - the crazy-ass games that this code is playing is clearly
messing not just with lockdep, it's messing with some very reasonable
spinlock sanity checks on UP (which just boil down to "a spinlock
should never have contention on UP")

Any chance of sanitizing this all?

                       Linus

> [ ? 12.526390] BUG: spinlock trylock failure on UP on CPU#0, scsi_id/543
> [ ? 12.528009] ?lock: f4ed8830, .magic: dead4ead, .owner: scsi_id/543, .owner_cpu: 0
> [ ? 12.528009] Pid: 543, comm: scsi_id Not tainted 3.3.0-rc2-main+ #21
> [ ? 12.528009] Call Trace:
> [ ? 12.528009] ?[<c043e56d>] spin_dump+0x6c/0x76
> [ ? 12.528009] ?[<c043e594>] spin_bug+0x1d/0x21
> [ ? 12.528009] ?[<c027739a>] do_raw_spin_trylock+0x33/0x38
> [ ? 12.528009] ?[<c04429c2>] _raw_spin_trylock+0x17/0x63
> [ ? 12.528009] ?[<c025fafa>] put_io_context+0xa1/0x10a
> [ ? 12.528009] ?[<c0269d85>] __cfq_slice_expired+0x2f6/0x319
> [ ? 12.528009] ?[<c026a8b2>] cfq_dispatch_requests+0x39/0x714
> [ ? 12.528009] ?[<c025b328>] elv_drain_elevator+0x3f/0x7d
> [ ? 12.528009] ?[<c025b3f0>] __elv_add_request+0x8a/0x169
> [ ? 12.528009] ?[<c02604a4>] blk_execute_rq_nowait+0x88/0xab
> [ ? 12.528009] ?[<c0260573>] blk_execute_rq+0xac/0xcd
> [ ? 12.528009] ?[<c0263cf5>] sg_io+0x23c/0x325
> [ ? 12.528009] ?[<c02642a3>] scsi_cmd_ioctl+0x1b1/0x332
> [ ? 12.528009] ?[<c0264452>] scsi_cmd_blk_ioctl+0x2e/0x38
> [ ? 12.528009] ?[<c035c15e>] sd_ioctl+0xd4/0xf4
> [ ? 12.528009] ?[<c02618ce>] __blkdev_driver_ioctl+0x26/0x2e
> [ ? 12.528009] ?[<c026226a>] blkdev_ioctl+0x70e/0x728
> [ ? 12.528009] ?[<c01b3f87>] block_ioctl+0x31/0x39
> [ ? 12.528009] ?[<c019ebb9>] do_vfs_ioctl+0x47b/0x4af
> [ ? 12.528009] ?[<c019ec2e>] sys_ioctl+0x41/0x63
> [ ? 12.528009] ?[<c0442c05>] syscall_call+0x7/0xb
>
> cu,
> ?-kp
--
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