Re: Reproducible SMP kernel deadlock in SCSI generic driver (sg)

From: Douglas Gilbert (
Date: Sun May 05 2002 - 12:45:04 EST

Jurgen Botz <>
> The sg module reproducibly deadlocks the kernel for me after some time
> of heavy I/O on an SMP system. This appears to be true in /all/ kernel
> versions... I can reproduce it very reliably now in 2.4.19-pre8 and
> 2.5.13, and I've had problems with CD ripping on my SMP workstation at
> least throughout the 2.4 series (I just never fully investigated before).
> The bug is almost certainly in sg.c; here is what I've narrowed down...

Which version of cdparanoia (or whatever) are you using?
You mention deadlock, is the machine completely locked
up or is sg and the device inoperable? Since sg doesn't
take any "big" locks (e.g. io_request_lock) then it
shouldn't be able to lock up your machine without help
(from other drivers).

Assuming you can still execute commands on your box after the
"deadlock", I'm interested in WCHAN from ps. Here are some
ps variants:
  ps -eo cmd,wchan
  ps -eo fname,tty,pid,stat,pcpu,wchan
  ps -eo pid,stat,pcpu,nwchan,wchan=WIDE-WCHAN-COLUMN -o args
The line for cdparanoia would be useful.

BTW ps needs to find the correct for
the WCHAN output to be relevant.

Doug Gilbert
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