Re: [BUG] XFS crash using Realtime Preemption patch

From: Nathaniel W. Filardo (nwf_at_andrew.cmu.edu)
Date: 12/24/04

  • Next message: Scott Mollica: "PROBLEM" 
    Date:	Thu, 23 Dec 2004 22:27:32 -0500 (EST)
To: Nathan Scott <nathans@sgi.com>

    On Thu, 23 Dec 2004, Nathan Scott wrote:

    > On Wed, Dec 22, 2004 at 02:50:20AM -0500, Nathaniel W. Filardo wrote:
    >> I added
    >> BUG_ON( (mrp->mr_writer != 0) && (mrp->mr_writer != 1) );
    >> to mrlock.h : mrunlock() to see if it was corruption and got the following
    >
    > Good thinkin.
    >
    >> instead. It's a similar call pathway, but somewhat different.
    >
    > Thats exactly the same call path right? There is no call to
    > down_trylock from xfs_iunlock (goes directly to up_write) so
    > I think that must just be leftover stack junk, and we should
    > assume the path was xfs_iunlock->(inline)mrunlock->up_write,
    > which means your BUG_ON didn't trigger... (put a printk of the
    > value there, maybe we'll get lucky and get some recognisable
    > hex pattern).

    If the BUG_ON didn't trigger, we shouldn't get a recognisable hex pattern
    - we'll get a 1 or a 0 every time, yes?

    I'll believe that it's the same trace. I changed the value for mr_writer
    in a writer state from 1 to 128 (leaving readers as 0) and got the same
    dump, which means that the new
             BUG_ON( (mrp->mr_writer != 0) && (mrp->mr_writer != 128 ) );
    didn't fire. So I don't think it's memory corruption unless my RAM is
    psychic. =)

    It looks like it might be a buggy attempt to upgrade a reader lock to a
    writer, or a more general failure of the locking semantics... Is the
    former possible along this path?

    >> kernel BUG at kernel/rt.c:1210!
    >> invalid operand: 0000 [#1]
    >> PREEMPT
    >> Modules linked in: uhci_hcd rtc eth1394 ohci1394 ieee1394 pcmcia
    >> hostap_pci hostap 8139too mii yenta_socket pcmcia_core ehci_hcd
    >> i2c_ali15x3 i2c_core ohci_hcd usbcore tun crc32
    >> CPU: 0
    >> EIP: 0060:[<c01308ac>] Not tainted VLI
    >> EFLAGS: 00010286 (2.6.10-rc3-mm1-V0.7.33-04-tcfq17)
    >> EIP is at up_write+0x8c/0xa0
    >> eax: 00000019 ebx: d039171c ecx: 00000000 edx: 00000000
    >> esi: 00000008 edi: d039168c ebp: 00000000 esp: cf8a6cdc
    >> ds: 007b es: 007b ss: 0068 preempt: 00000001
    >> Process rm (pid: 8661, threadinfo=cf8a6000 task=d5014370)
    >> Stack: c0357dbb c035a1f6 000004ba c0130ddf 00000010 00000286 d039171c
    >> c01d2d8c
    >> cf8a6000 d038dec8 d020bb44 d039168c d038dec8 d020bb44 c01d735c
    >> cf8a6d38
    >> cf8a6d3c 00000000 00000000 d6c3eb4c 00000000 d6c3ec00 00000002
    >> c7af1700
    >> Call Trace:
    >> [<c0130ddf>] down_trylock+0x1f/0xb0 (16)
    >> [<c01d2d8c>] xfs_iunlock+0x6c/0x130 (16)
    >> [<c01d735c>] xfs_iflush+0x1cc/0x440 (28)
    >
    > --
    > Nathan
    >
    >
    -
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