Re: [9fans] self inflicted gunshot wound

[erik quanstrom <quanstro@quanstro.net>]

On Tue Apr  7 21:50:14 EDT 2009, rsc@swtch.com wrote:
> > abort()+0x0 /sys/src/libc/9sys/abort.c:6
> > plumbpackattr(attr=0x28b00)+0x126 /sys/src/libplumb/mesg.c:125
> >        n=0x93
> >        a=0x3e990
> >        s=0x3a430
> >        t=0x3a497
>
> t is unlikely to be correct here; it would have been saved
> at the last call to strlen but since then got +='ed with the result.
>
> > acid: regs()
> > PC      0x0000c80c abort  /sys/src/libc/9sys/abort.c:6
> > SP      0x00068e78 ECODE 0x00000004 EFLAG 0x00000206
> > CS      0x00000023 DS    0x0000001b SS  0x0000001b
> > GS      0x0000001b FS    0x0000001b ES  0x0000001b
> > TRAP    0x0000000e page fault
> > AX      0x0003a4c3 BX   0x0003a4c6 CX   0x0003a430 DX   0x00000093
> > DI      0x0003a4c7 SI   0x0003ea19 BP   0x0003e9f0
>
> there's s+n in AX.  t is likely to be BX or DI, judging from the
> pointer values; it has either written 3 or 4 bytes past the
> end of the allocated section, which explains the abort.
> you'd have to disassemble plumbpackattr to make sure.
> it would be interesting to print *(*plumbpackattr:s\s)
> to see if the string is corrupted.

acid: *(*plumbpackattr:s\s)
filetype=mail sender=xxxx@xxxx.xxx length=8749 mailtype=delete date='Sun Mar4de7153cecd4a9b45aead1clfs digest=aff98fb56526d94ab768adbc93d12d989a11ed53

hmmm.  i think you might be on to something after all.
maybe it was fratricide.

> i don't understand what you mean.
> plumbers clients are always waiting for something
> to happen.  the plumber's only job is to tell them
> when it does.

several were waiting on something else to happen; they were
sleeping waiting for an exclusive-open file.  the only reason
i mentioned it is that may have been 5 minutes between the
time that plumber tried to write the message and when it
could be delivered.

> i suspect the global buffer in plumbpackattr's quote.
> if you had multiple threads running through
> plumbpackattr at once, it might cause the kind of crash you saw.
> all the ordinary plumbing is protected by the QLock named queue,
> but it looks like maybe if you'd been writing the rules file
> at exactly the same time, that might have triggered
> a simultaneous plumbpackattr call.

unfortunately, i was not writing the rules file, that i know of.

- erik