Messages in this thread | | | Subject | Re: Process Hang in __read_seqcount_begin | From | Eric Dumazet <> | Date | Mon, 22 Oct 2012 19:01:39 +0200 |
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On Mon, 2012-10-22 at 09:46 -0700, Peter LaDow wrote: > I posted this problem some time back on the linux-rt-users and > netfilter lists. Since then, we thought we had a workaround to avoid > this problem, so we dropped the issue. But now 5 months later, the > problem has reappeared. And this time it is much more serious and > much more difficult to re-create. After perusing both those lists, > I'm not sure if those were the proper places to post. The netfilter > list seems to be more focused on the user space side of things, and > the RT page indicates that kernel side RT issues should go to lkml. > > Anyway, here's a repost of that problem from July. Perhaps somebody > here can point us in the right direction. > > We are running 3.0.36-rt57 on a powerpc box. During some testing with > heavy loads and interfaces coming up/going down (specifically PPP), we > have run into a case where iptables hangs and cannot be killed. It > requires a reboot to fix the problem. > > Connecting the BDI and debugging the kernel, we get: > > #0 get_counters (t=0xdd5145a0, counters=0xe3458000) > at include/linux/seqlock.h:66 > #1 0xc026b4ac in do_ipt_get_ctl (sk=<value optimized out>, > cmd=<value optimized out>, user=0x10612078, len=<value optimized out>) > at net/ipv4/netfilter/ip_tables.c:918 > #2 0xc022226c in nf_sockopt (sk=<value optimized out>, pf=2 '\002', > val=<value optimized out>, opt=<value optimized out>, len=0xdd4c7d4c, > get=1) at net/netfilter/nf_sockopt.c:109 > #3 0xc0236b1c in ip_getsockopt (sk=0xdf071480, level=<value optimized out>, > optname=65, optval=0x10612078 <Address 0x10612078 out of bounds>, > optlen=0xbfbe0c2c) at net/ipv4/ip_sockglue.c:1308 > #4 0xc02522a8 in raw_getsockopt (sk=0xdf071480, level=<value optimized out>, > optname=<value optimized out>, optval=<value optimized out>, > optlen=<value optimized out>) at net/ipv4/raw.c:811 > #5 0xc01f4c38 in sock_common_getsockopt (sock=<value optimized out>, > level=<value optimized out>, optname=<value optimized out>, > optval=<value optimized out>, optlen=<value optimized out>) > at net/core/sock.c:2157 > #6 0xc01f2df8 in sys_getsockopt (fd=<value optimized out>, level=0, > optname=65, optval=0x10612078 <Address 0x10612078 out of bounds>, > optlen=0xbfbe0c2c) at net/socket.c:1839 > #7 0xc01f45b4 in sys_socketcall (call=15, args=<value optimized out>) > at net/socket.c:2421 > > It seems to be stuck in __read_seqcount_begin. From include/linux/seqlock.h: > > static inline unsigned __read_seqcount_begin(const seqcount_t *s) > { > unsigned ret; > > repeat: > ret = ACCESS_ONCE(s->sequence); > if (unlikely(ret & 1)) { > cpu_relax(); > <----- It is always here > goto repeat; > } > return ret; > } > > I've been scouring the mailing lists and Google searches trying to > find something, but thus far have come up with nothing. > > Any tips would be appreciated.
This looks like a corruption of s->sequence, and is value is odd, even if no writer is alive.
Does local_bh_disable() disables preemption on RT ?
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