Re: 3.14-rc2 XFS backtrace because irqs_disabled.

Al Viro
2014-02-14T16:16:34Z

On Fri, Feb 14, 2014 at 08:13:02AM -0800, Christoph Hellwig wrote:
> On Wed, Feb 12, 2014 at 01:32:55PM -0800, Linus Torvalds wrote:
> > We'd have to teach each user of "dequeue_signal()" to free the siginfo
> > thing. Which shouldn't be too bad - I think we've collected all of
> > that into generic code, and there isn't the mass or architecture code
> > that knows about these things any more. But there are a few odd
> > drivers etc and signalfd.
>
> The few odd drivers are nbd, jffs2 and the usb mass storage gadget.
> All of these have in common that they try to handle signals in a kernel
> thread (which we don't even allow by default), and that they ignore the
> siginfo. I think they could mostly be replaced by an addition to the
> kthread API to allow a kthread to be killed by signals for legacy
> reasons.

FWIW, there's a funny situation - all users of dequeue_signal_lock()
actually ignore info completely. I'm not saying that we ought to
stop returning it, but e.g. jbd part of that patch is simply
diff --git a/fs/jffs2/background.c b/fs/jffs2/background.c
index 2b60ce1..aefdff2 100644
--- a/fs/jffs2/background.c
+++ b/fs/jffs2/background.c
@@ -119,13 +119,14 @@ static int jffs2_garbage_collect_thread(void *_c)
/* Put_super will send a SIGKILL and then wait on the sem.
*/
while (signal_pending(current) || freezing(current)) {
- siginfo_t info;
+ ksiginfo_t info;
unsigned long signr;

if (try_to_freeze())
goto again;

signr = dequeue_signal_lock(current, &current->blocked, &info);
+ dismiss_siginfo(&info);

switch(signr) {
case SIGSTOP:

Not complicated at all. Where it does get complicated is ->last_siginfo and
PTRACE_SETSIGINFO - getting that reasonably clean is what I'm still fighting
right now...