select + signal + truss => LOR

[Don Lewis]

I don't believe I've seen any reports of this particular lock order
reversal.  I got it by pointing truss at syslogd.  My kernel and world
were built from a cvsup run slightly before Fri Nov  7 14:50:18 PST
2003.


 Sleeping on "stopevent" with the following non-sleepable locks held:
exclusive sleep mutex sigacts r = 0 (0xc6bc0aa8) locked @ /usr/src/sys/kern/kern
_condvar.c:289
lock order reversal
 1st 0xc6bc0aa8 sigacts (sigacts) @ /usr/src/sys/kern/kern_condvar.c:289
 2nd 0xc6bbabc4 process lock (process lock) @ /usr/src/sys/kern/kern_synch.c:309
Stack backtrace:
backtrace(c08a4327,c6bbabc4,c08a0922,c08a0922,c08a1964) at backtrace+0x17
witness_lock(c6bbabc4,8,c08a1964,135,c08a05a9) at witness_lock+0x672
_mtx_lock_flags(c6bbabc4,0,c08a1964,135,ffffffff) at _mtx_lock_flags+0xba
msleep(c6bbac98,c6bbabc4,5c,c08a4b24,0) at msleep+0x794
stopevent(c6bbab58,2,e,822,c096d440) at stopevent+0x85
issignal(c6bbbb40,2,c08a1463,bd,c6bbab58) at issignal+0x168
cursig(c6bbbb40,0,c089e483,121,0) at cursig+0xf0
cv_wait_sig(c0991f34,c0991f00,c08a492e,348,4) at cv_wait_sig+0x448
kern_select(c6bbbb40,7,8055060,0,0) at kern_select+0x526
select(c6bbbb40,e5f26d10,c08bea62,3ee,5) at select+0x66
syscall(2f,2f,2f,8,1) at syscall+0x2c0
Xint0x80_syscall() at Xint0x80_syscall+0x1d
--- syscall (93), eip = 0x480d03ff, esp = 0xbfbff79c, ebp = 0xbfbffd98 ---
Sleeping on "stopevent" with the following non-sleepable locks held:
exclusive sleep mutex sigacts r = 0 (0xc6bc0aa8) locked @ /usr/src/sys/kern/subr
_trap.c:260
Sleeping on "stopevent" with the following non-sleepable locks held:
exclusive sleep mutex sigacts r = 0 (0xc6bc0aa8) locked @ /usr/src/sys/kern/subr
_trap.c:260