On Wed 06-01-16 15:48:36, Sergey Senozhatsky wrote:
> On (01/05/16 15:37), Jan Kara wrote:
> > > How about setting 'sync_print' to 'true' in...
> > > bust_spinlocks() /* only set to true */
> > > or
> > > console_verbose() /* um... may be... */
> > > or
> > > having a separate one-liner for that
> > >
> > > void console_panic_mode(void)
> > > {
> > > sync_print = true;
> > > }
> > >
> > > and call it early in panic(), before we send out IPI_STOP.
> >
> > I like using console_verbose() for setting sync_print to true. That will
> > likely be more reliable than using oops in progress. After all
> > console_verbose() is used like console_panic_mode() anyway and in quite a
> > few places so it is a reasonable match.
>
> another corner case.
>
> a quote from -mm a74b6533ead8
> http://www.spinics.net/lists/linux-mm/msg98990.html
>
> : This patch reduces the probability of such a lockup by introducing a
> : specialized kernel thread (oom_reaper) which tries to reclaim additional
> : memory by preemptively reaping the anonymous or swapped out memory owned
> : by the oom victim under an assumption that such a memory won't be needed
> : when its owner is killed and kicked from the userspace anyway. There is
> : one notable exception to this, though, if the OOM victim was in the
> : process of coredumping the result would be incomplete. This is
> considered
> : a reasonable constrain because the overall system health is more
> important
> : than debugability of a particular application.
> :
> : A kernel thread has been chosen because we need a reliable way of
> : invocation so workqueue context is not appropriate because all the
> workers
> : might be busy (e.g. allocating memory). Kswapd which sounds like
> another
> : good fit is not appropriate as well because it might get blocked on locks
> : during reclaim as well.
>
> particularly this "workqueue context is not appropriate because all the
> workers
> might be busy (e.g. allocating memory)" part. I think printk should switch to
> sync mode in this case, since printk now does queue_work(system_wq, work).
> um... console_verbose() call from oom kill? but it'll be nice to return back
> to async mode once (if) memory pressure goes away.
Hum, yes, some mechanism to switch to sync printing in case work cannot be
executed for a long time is probably needed. I'll think about it.
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
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