Re: kqueue LOR

On Thu, Feb 08, 2007 at 09:49:23PM +0100, Frode Nordahl wrote:
> On 27. nov. 2006, at 10.21, Kostik Belousov wrote:
> 
> >On Sun, Nov 26, 2006 at 09:30:39AM +0100, V??clav Haisman wrote:
> >>Hi,
> >>the attached lor.txt contains LOR I got this yesterday. It is  
> >>FreeBSD 6.1
> >>with relatively recent kernel, from last week or so.
> >>
> >>--
> >>VH
> >
> >>+lock order reversal:
> >>+ 1st 0xc537f300 kqueue (kqueue) _at_ /usr/src/sys/kern/kern_event.c: 
> >>1547
> >>+ 2nd 0xc45c22dc struct mount mtx (struct mount mtx) _at_ /usr/src/ 
> >>sys/ufs/ufs/ufs_vnops.c:138
> >>+KDB: stack backtrace:
> >>+kdb_backtrace(c07f9879,c45c22dc,c07fd31c,c07fd31c,c080c7b2,...)  
> >>at kdb_backtrace+0x2f
> >>+witness_checkorder(c45c22dc,9,c080c7b2,8a,c07fc6bd,...) at  
> >>witness_checkorder+0x5fe
> >>+_mtx_lock_flags(c45c22dc,0,c080c7b2,8a,e790ba20,...) at  
> >>_mtx_lock_flags+0x32
> >>+ufs_itimes(c47a0dd0,c47a0e90,e790ba78,c060e1cc,c47a0dd0,...) at  
> >>ufs_itimes+0x6c
> >>+ufs_getattr(e790ba54,e790baec,c0622af6,c0896f40,e790ba54,...) at  
> >>ufs_getattr+0x20
> >>+VOP_GETATTR_APV(c0896f40,e790ba54,c08a5760,c47a0dd0,e790ba74,...)  
> >>at VOP_GETATTR_APV+0x3a
> >>+filt_vfsread(c4cf261c,6,c07f445e,60b,0,...) at filt_vfsread+0x75
> >>+knote(c4f57114,6,1,1f30c2af,1f30c2af,...) at knote+0x75
> >>+VOP_WRITE_APV(c0896f40,e790bbec,c47a0dd0,227,e790bcb4,...) at  
> >>VOP_WRITE_APV+0x148
> >>+vn_write(c45d5120,e790bcb4,c5802a00,0,c4b73a80,...) at vn_write 
> >>+0x201
> >>+dofilewrite(c4b73a80,1b,c45d5120,e790bcb4,ffffffff,...) at  
> >>dofilewrite+0x84
> >>+kern_writev(c4b73a80,1b,e790bcb4,8220c71,0,...) at kern_writev+0x65
> >>+write(c4b73a80,e790bd04,c,c07d899c,3,...) at write+0x4f
> >>+syscall(3b,3b,bfbf003b,0,bfbfeae4,...) at syscall+0x295
> >>+Xint0x80_syscall() at Xint0x80_syscall+0x1f
> >>+--- syscall (4, FreeBSD ELF32, write), eip = 0x2831d727, esp =  
> >>0xbfbfea1c, ebp = 0xbfbfea48 ---
> >
> >Thank you for the report. The LOR is caused by my commit into
> >sys/ufs/ufs/ufs_vnops.c, rev. 1.280.
> 
> While debugging a problem I have with 6.2-RELEASE on one of my  
> servers I saw this LOR. After being up for a short while the server  
> freezes, not responding to serial console, network og keyboard. I  
> can't even get to DDB by sending BREAK on the serial console.
> 
> Enabling INVARIANTS, INVARIANT_SUPPORT, WITNESS and WITNESS_SKIPSPIN  
> did not give more information about the freeze other than printing  
> the LOR now and then.
The useful way to report deadlock is described in developer handbook,
kernel debug chapter, deadlock debugging. If the freeze caused by this LOR,
then supplying me with information requested in that chapter could be
helpful (both to you and me).