On Tue, 6 May 2014 16:37:14 -0700 Andrew Morton <a...@linux-foundation.org> wrote:
> What I have in -next is very different from this version of the patch. > What's happening? Hmm, it looks massaged from what I originally sent in order to be placed after the other patches in the series. A quick review of the patch seems to be mostly the same logic, but it is a bit different. Jan, did you update my patch? > > > From: Steven Rostedt <rost...@goodmis.org> > Subject: printk: remove separate printk_sched buffers and use printk buf > instead > > To prevent deadlocks with doing a printk inside the scheduler, > printk_sched() was created. The issue is that printk has a console_sem > that it can grab and release. The release does a wake up if there's a > task pending on the sem, and this wake up grabs the rq locks that is held > in the scheduler. This leads to a possible deadlock if the wake up uses > the same rq as the one with the rq lock held already. > > What printk_sched() does is to save the printk write in a per cpu buffer > and sets the PRINTK_PENDING_SCHED flag. On a timer tick, if this flag is > set, the printk() is done against the buffer. > > There's a couple of issues with this approach. > > 1) If two printk_sched()s are called before the tick, the second one > will overwrite the first one. > > 2) The temporary buffer is 512 bytes and is per cpu. This is a quite a > bit of space wasted for something that is seldom used. > > In order to remove this, the printk_sched() can use the printk buffer > instead, and delay the console_trylock()/console_unlock() to the queued > work. > > Because printk_sched() would then be taking the logbuf_lock, the > logbuf_lock must not be held while doing anything that may call into the > scheduler functions, which includes wake ups. Unfortunately, printk() > also has a console_sem that it uses, and on release, the up(&console_sem) > may do a wake up of any pending waiters. This must be avoided while > holding the logbuf_lock. > > Signed-off-by: Steven Rostedt <rost...@goodmis.org> Jan, if you did massage my patch, you should add here what you did. Usually in [brackets]. Otherwise it puts the blame on me if something breaks, or adds confusion if I happen to send out another patch like I just did. -- Steve > Signed-off-by: Jan Kara <j...@suse.cz> > Signed-off-by: Andrew Morton <a...@linux-foundation.org> > --- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
