Re: [BUG] Panic in smp_call_function_interrupt

[Jean-Marc Saffroy]

On Tue, 16 Jan 2001, I wrote:

> [root@picasso /]# dd if=/dev/sda of=/dev/null

[ causes an oops on our SMP machines ]

> This is a 2.4.0 (release) with kdb 1.7 for 2.4.0. I tried the same on a
> similar machine with 2 CPUs and without kdb, it gave the same result. A
> 2.4.0 without SMP support on these machines has no problem.

I have applied the 2.4.1 pre8 patch, and the oops is still here.

> Can anyone reproduce this ? Or maybe it has already been fixed ?

I have made more tests, and I have also observed (twice) a deadlock
instead of the usual oops. From what I saw, the usual scenario is that the
dd (actually a read of /dev/sda is enough) makes the buffer cache grow
larger and larger, until the system tries to free pages, and that's when
things seem to go wrong. Whether I get a deadlock or an oops, kdb shows me
one processor with a call stack like this :

[1]kdb> bt
    EBP       EIP         Function(args)
0xc1157eac 0xc0110cc3 smp_call_function+0x9f (0xc012a7ac, 0xc1157ef8, 0x1,
0x1, 0xc1157ef8)
0xc1157ed0 0xc012a77f smp_call_function_all_cpus+0x1b (0xc012a7ac,
0xc1157ef8, 0xc111f400)
0xc1157f7c 0xc012a846 drain_cpu_caches+0x52 (0xc111f400)
0xc1157f8c 0xc012a8cd __kmem_cache_shrink+0xd (0xc111f400)
0xc1157f9c 0xc012a97c kmem_cache_shrink+0x54 (0xc111f400, 0x0)
0xc1157fac 0xc0148bc5 shrink_icache_memory+0x2d (0x6, 0x4, 0x6, 0x4)
0xc1157fd0 0xc012d6ba do_try_to_free_pages+0x6a (0x4, 0x0, 0xc1171fa0,
0xc0105000)
0xc1157fec 0xc012d742 kswapd+0x6e

When an oops occurs, it is on another CPU, in smp_call_function_interrupt:
this functions tries to jump to a NULL address. But if I look at the
call_data struct, it seems ok (ie, ptr to func is not NULL).

When it is a deadlock, all CPUs other than the one with the stack above
are in default_idle, and the CPU in smp_call_function() loops forever in:

	while (atomic_read(&data.started) != cpus)
		barrier();

So I guess that there is some sort of race condition, but I don't know
where. Any idea ?

Regards,

-- 
Jean-Marc Saffroy - Research Engineer - Silicomp Research Institute
mailto:[e-mail]