Date: Fri, 01 Feb 2008 06:20:55 -0600 From: Eric Anderson <anderson@freebsd.org> To: Steven Hartland <killing@multiplay.co.uk> Cc: Dieter <freebsd@sopwith.solgatos.com>, freebsd-performance@freebsd.org Subject: Re: newfs locks entire machine for 20seconds Message-ID: <47A30EA7.7050506@freebsd.org> In-Reply-To: <002201c86499$7861ac20$b6db87d4@multiplay.co.uk> References: <200801310147.BAA04522@sopwith.solgatos.com> <47A2A606.9080702@freebsd.org> <002201c86499$7861ac20$b6db87d4@multiplay.co.uk>
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Steven Hartland wrote:
>
> ----- Original Message ----- From: "Eric Anderson" <anderson@freebsd.org>
>
>> I saw this once before, a long time back, and every time I went
>> through a debugging session, it came to some kind of lock on the
>> sysctl tree with regards to the geom info (maybe the XML kind of tree
>> dump or something). I don't recall all the details, but it was
>> something like that.
>
> Yep thats where I've traced it to its requesting: kern.geom.confxml
>
> Which does:-
> static int
> sysctl_kern_geom_confxml(SYSCTL_HANDLER_ARGS)
> {
> int error;
> struct sbuf *sb;
>
> sb = sbuf_new(NULL, NULL, 0, SBUF_AUTOEXTEND);
> g_waitfor_event(g_confxml, sb, M_WAITOK, NULL);
> error = SYSCTL_OUT(req, sbuf_data(sb), sbuf_len(sb) + 1);
> sbuf_delete(sb);
> return error;
> }
>
> What I dont understand is why this would lock the entire machine.
>
> I've enabled LOCK_PROFILING and reran and I get the following which
> seems to indicate the culpret is: SYSCTL_LOCK()
>
> From what I can tell g_waitfor_event is returning EAGAIN for a large
> amount of time which means we get stuck in:-
> userland_sysctl
> ...
> SYSCTL_LOCK();
>
> do {
> req.oldidx = 0;
> req.newidx = 0;
> error = sysctl_root(0, name, namelen, &req);
> } while (error == EAGAIN);
>
> if (req.lock == REQ_WIRED && req.validlen > 0)
> vsunlock(req.oldptr, req.validlen);
>
> SYSCTL_UNLOCK();
> ...
>
> The only reason I can see for returning EAGAIN is g_destroy_geom
> calling g_cancel_event
Wait - if it returns EAGAIN for a while, then look at that code above.
It will hold the sysctl lock for some indefinite amount of time. Maybe
it should look like this instead:
do {
SYSCTL_LOCK();
req.oldidx = 0;
req.newidx = 0;
error = sysctl_root(0, name, namelen, &req);
SYSCTL_UNLOCK();
} while (error == EAGAIN);
if (req.lock == REQ_WIRED && req.validlen > 0)
vsunlock(req.oldptr, req.validlen);
Can you try that?
Eric
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