Re: [BUG] XFS crash using Realtime Preemption patch

[Nathaniel W. Filardo]

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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/