RE: kthread_exit and giant

On 05-May-2003 Petri Helenius wrote:
> I´ve been bouncing this with Soren a few roundtrips and I thought I´ll ask a wider
> audience since I could not locate the information who would be responsible for
> grabbing Giant in this case, but it seems to be required to hold it when the thread
> exits; (the panic occurs when ATA RAID rebuild thread completes)

The kthread is supposed to acquire Giant before calling kthread_exit().
Actually, my guess is that the ar kthread needs to acquire Giant for the
lifetime of the thread.  I have an untested patch locally:


Index: ata-raid.c
===================================================================
RCS file: /usr/cvs/src/sys/dev/ata/ata-raid.c,v
retrieving revision 1.64
diff -u -r1.64 ata-raid.c
--- ata-raid.c  4 May 2003 16:17:54 -0000       1.64
+++ ata-raid.c  5 May 2003 18:15:35 -0000
_at__at_ -969,6 +969,7 _at__at_
     int disk, s, count = 0, error = 0;
     caddr_t buffer;
 
+    mtx_lock(&Giant);
     if ((rdp->flags & (AR_F_READY|AR_F_DEGRADED)) != (AR_F_READY|AR_F_DEGRADED))
        kthread_exit(EEXIST);

 
> FreeBSD 5.0-CURRENT #3: Sat May  3 11:09:45 GMT 2003
>     root_at_kompak.vuokselantie10.fi:/usr/src/sys/i386/compile/EMTEST
> kompak# atacontrol status 0
> ar0: ATA RAID1 subdisks: ad4 ad6 status: REBUILDING 44% completed
> kompak# panic: mutex Giant not owned at ../../../kern/kern_exit.c:122
> Debugger("panic")
> Stopped at      Debugger+0x54:  xchgl   %ebx,in_Debugger.0
> db> trace
> Debugger(c038d044,c03eedc0,c038c78b,d26f4c54,1) at Debugger+0x54
> panic(c038c78b,c038c8c4,c038acdf,7a,104) at panic+0xab
> _mtx_assert(c03ed140,1,c038acdf,7a,85) at _mtx_assert+0xec
> exit1(c2a075f0,0,85,84,2) at exit1+0x33
> kthread_exit(0,1,1,0,0) at kthread_exit+0xb6
> ar_rebuild(c25e3000,d26f4d48,c038ad90,310,c2a075f0) at ar_rebuild+0x445
> fork_exit(c0161c40,c25e3000,d26f4d48) at fork_exit+0xc0
> fork_trampoline() at fork_trampoline+0x1a
> --- trap 0x1, eip = 0, esp = 0xd26f4d7c, ebp = 0 ---
> db>

-- 

John Baldwin <jhb_at_FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/