Re: pipe mutex vs. sigio lock lock order reversal

2002-07-11 Thread Don Lewis 

On  7 Jul, Don Lewis wrote:
 This error showed up in my logs this morning while I was building some
 ports on a uni-processor box. I'm running a version of -current from
 July 7 about 1 AM PDT.
 
 Jul  7 07:47:09 scratch kernel: lock order reversal
 Jul  7 07:47:09 scratch kernel: 1st 0xcabf7980 pipe mutex (pipe mutex) @ 
/usr/src/sys/kern/sys_pipe.c:451
 Jul  7 07:47:09 scratch kernel: 2nd 0xc0474300 sigio lock (sigio lock) @ 
/usr/src/sys/kern/kern_sig.c:2113 

I figured out part of the problem.  The call stack is:

pgsigio()
pipe_read()
dofileread()
read()

This was a bit tricky to find because the call to pgsigio() is hidden
in pipeselwakeup(), which is an inline function called by pipe_read().

I don't see a good way to fix this.  I also don't yet know why
witness thinks it has seen the locks asserted in the opposite order.


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Re: pipe mutex vs. sigio lock lock order reversal

2002-07-11 Thread Don Lewis 

On 11 Jul, Don Lewis wrote:
 On  7 Jul, Don Lewis wrote:

 Jul  7 07:47:09 scratch kernel: lock order reversal
 Jul  7 07:47:09 scratch kernel: 1st 0xcabf7980 pipe mutex (pipe mutex) @ 
/usr/src/sys/kern/sys_pipe.c:451
 Jul  7 07:47:09 scratch kernel: 2nd 0xc0474300 sigio lock (sigio lock) @ 
/usr/src/sys/kern/kern_sig.c:2113 
 
 I figured out part of the problem.  The call stack is:
 
 pgsigio()
 pipe_read()
 dofileread()
 read()
 
 This was a bit tricky to find because the call to pgsigio() is hidden
 in pipeselwakeup(), which is an inline function called by pipe_read().
 
 I don't see a good way to fix this.  I also don't yet know why
 witness thinks it has seen the locks asserted in the opposite order.

I got the serial console stuff set up and did a show witness to find
the conflicting lock order:

sigio - process group - process - filedesc - pipe

I think the best fix is to defer calling pgsigio until after the pipe
lock is released, but this looks like a messy change.


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