cvs commit: src/sys/kern kern_exit.c (DEVFS bug) ?

[Martin Blapp]

Hi all,

The kernel I've made with 'mtx_assert(&Giant, MA_OWNED);' in all tty functions
works fine. I'm not able to crash it yet, even under 24 hour load.

> But I have also seen what appears to be strange interactions or races between 
> devfs and the TTY code before the Giant push down here, which was causing me 
> some problems. After some discussions with John and Bruce, it looks like the 
> manipulation of t_session should be protected by Giant.

I Agree. This backout doesn't solve this panic here. I got this panic on FreeBSD 
5.3 RELEASE and  5.4 RELEASE too. Exactly the same trace. And revision 1.272 
never made it into RELENG_5.

#1  0xc066355e in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:409
#2  0xc06638b5 in panic (fmt=0xc0891732 "%s") at /usr/src/sys/kern/kern_shutdown.c:565
#3  0xc085c6b6 in trap_fatal (frame=0xed6e4ab8, eva=4) at /usr/src/sys/i386/i386/trap.c:836
#4  0xc085c3bf in trap_pfault (frame=0xed6e4ab8, usermode=0, eva=4) at /usr/src/sys/i386/i386/trap.c:744
#5  0xc085bfb5 in trap (frame=
       {tf_fs = 8, tf_es = 40, tf_ds = -1063714776, tf_edi = -1064042304, tf_esi 
= 0, tf_ebp = -311538944, tf_isp = -311538972, tf_ebx
= -967615488, tf_edx = -1063651212, tf_ecx = -941099136, tf_eax = 0, tf_trapno = 
12, tf_err = 0, tf_eip = -1066845359, tf_cs = 32,
tf_eflags = 66194, tf_esp = -967615488, tf_ss = 0})
     at /usr/src/sys/i386/i386/trap.c:434
#6  0xc0848bea in calltrap () at /usr/src/sys/i386/i386/exception.s:139
#7  0xc0693b51 in ttymodem (tp=0xc6535c00, flag=-1063651212) at /usr/src/sys/kern/tty.c:1659
#8  0xc0698362 in ptcclose (dev=0x0, flags=3, fmt=8192, td=0xc7e7f780) at linedisc.h:136
#9  0xc0638a6f in giant_close (dev=0xcb3c1100, fflag=3, devtype=8192, td=0xc7e7f780) at /usr/src/sys/kern/kern_conf.c:266
#10 0xc06162bf in devfs_close (ap=0xed6e4b7c) at /usr/src/sys/fs/devfs/devfs_vnops.c:287
#11 0xc086dc1c in VOP_CLOSE_APV (vop=0x0, a=0xc099f874) at vnode_if.c:426
#12 0xc06c87e2 in vn_close (vp=0xc9cdf660, flags=3, file_cred=0x0, td=0xc7e7f780) at vnode_if.h:227
#13 0xc06c974a in vn_closefile (fp=0xc6fc5438, td=0xc7e7f780) at /usr/src/sys/kern/vfs_vnops.c:865
#14 0xc06162e7 in devfs_close_f (fp=0xc6fc5438, td=0xc7e7f780) at /usr/src/sys/fs/devfs/devfs_vnops.c:297
#15 0xc0642cdc in fdrop_locked (fp=0xc6fc5438, td=0xc7e7f780) at file.h:295
#16 0xc0642c29 in fdrop (fp=0xc6fc5438, td=0xc7e7f780) at /usr/src/sys/kern/kern_descrip.c:2122
#17 0xc06411c7 in closef (fp=0xc6fc5438, td=0xc7e7f780) at /usr/src/sys/kern/kern_descrip.c:1942
#18 0xc063e329 in close (td=0xc7e7f780, uap=0x0) at /usr/src/sys/kern/kern_descrip.c:1007

>  Back out one of the Giant removals from revision 1.272. Giant was not here to
>  protect the vnode, it was present to synchronize access to TTY session
>  information between exit(2) and the TTY code. While we are here, note that
>  Giant is required for TTY protection.
>
>  Clue from:      bde
>  Discussed with: jhb
>  MFC after:      1 week
>
>  Revision  Changes    Path
>  1.290     +2 -2      src/sys/kern/kern_exit.c
>