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SubjectRe: 2.6.28-rc2 hates my e1000e

[ Note, lots of family activities this weekend, so my response may be
slow ]

On Sat, 1 Nov 2008, Linus Torvalds wrote:
> On Sat, 1 Nov 2008, Jonathan Corbet wrote:
>
> > Networking is fine in the absence of NFS. I retried things and
> > stress-tested it in a few ways with no trouble. I think your last patch
> > fixes the network card just fine.
> >
> > Then I tried NFS again, watching more closely this time around.
> > Everything locks up. In fact, the soft lockup watchdog starts to
> > scream:
>
> Interesting. I wonder why it happens for NFS, but not apparently for all
> your other modules.
>
> It does look very much like a ftrace issue, though, not NFS or
> network-related. Steven? Is this something that you are aware of already,
> with what looks like a lockup in ftrace_record_ip()?
>

No, I have not seen this before. The code is now pretty straight forward.

Jon, could you do a gdb vmlinux and a li *ftrace_record_ip+0xcb to find
the exact line that is?

Showing the call path of this we have:

in module.c:

/* sechdrs[0].sh_size is always zero */
mseg = section_objs(hdr, sechdrs, secstrings, "__mcount_loc",
sizeof(*mseg), &num_mcount);
ftrace_init_module(mseg, mseg + num_mcount);

Where we pass a table of mcount callers to the ftrace_init_module.

void ftrace_init_module(unsigned long *start, unsigned long *end)
{
if (ftrace_disabled || start == end)
return;
ftrace_convert_nops(start, end);
}

I wonder if I should test to make sure start is < end :-/

ftrace_convert_nops does the following under a mutex.

while (p < end) {
addr = ftrace_call_adjust(*p++);
ftrace_record_ip(addr);
}


And ftrace_record_ip does:

ftrace_record_ip(unsigned long ip)
{
struct dyn_ftrace *rec;
if (!ftrace_enabled || ftrace_disabled)
return NULL;
rec = ftrace_alloc_dyn_node(ip);
if (!rec)
return NULL;
rec->ip = ip;
list_add(&rec->list, &ftrace_new_addrs);
return rec;
}


The ftrace_alloc_dyn_node does allocate a page if we are running low, but
there's no other loops or locks that I can see us deadlocking on.

-- Steve



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