From: Michal Hocko <mhocko@suse.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>,
tglx@linutronix.de, ying.huang@intel.com, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm, swap: don't disable preemption while taking the per-CPU cache
Date: Fri, 23 Jun 2017 14:13:42 +0200 [thread overview]
Message-ID: <20170623121342.GT5308@dhcp22.suse.cz> (raw)
In-Reply-To: <20170623120842.oai2kiqkxz5jx6nh@linutronix.de>
On Fri 23-06-17 14:08:42, Sebastian Andrzej Siewior wrote:
> On 2017-06-23 14:02:33 [+0200], Michal Hocko wrote:
> > On Fri 23-06-17 13:47:55, Sebastian Andrzej Siewior wrote:
> > > get_cpu_var() disables preemption and returns the per-CPU version of the
> > > variable. Disabling preemption is useful to ensure atomic access to the
> > > variable within the critical section.
> > > In this case however, after the per-CPU version of the variable is
> > > obtained the ->free_lock is acquired. For that reason it seems the raw
> > > accessor could be used. It only seems that ->slots_ret should be
> > > retested (because with disabled preemption this variable can not be set
> > > to NULL otherwise).
> > > This popped up during PREEMPT-RT testing because it tries to take
> > > spinlocks in a preempt disabled section.
> >
> > Ohh, because the spinlock can sleep with PREEMPT-RT right? Don't we have
> yup.
>
> > much more places like that? It is perfectly valid to take a spinlock
> well we have more than just this one patch to fix things like that :)
> The easy/simple things (like this one which is valid in RT and !RT) I
> try to push upstream asap and the other remain in the RT tree.
yeah, makes sense to me.
> > while the preemption is disabled. E.g. we do take ptl lock inside
> > kmap_atomic sections which disables preemption on 32b systems.
> we don't disable preemption in kmap_atomic(). It would be bad :)
Ohh, I didn't know about that.
> > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> >
> > Acked-by: Michal Hocko <mhocko@suse.com>
> Thanks.
>
> Sebastian
--
Michal Hocko
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
prev parent reply other threads:[~2017-06-23 12:13 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-23 10:12 [RFC PATCH] " Sebastian Andrzej Siewior
2017-06-23 10:34 ` Michal Hocko
2017-06-23 11:47 ` [PATCH] " Sebastian Andrzej Siewior
2017-06-23 12:02 ` Michal Hocko
2017-06-23 12:08 ` Sebastian Andrzej Siewior
2017-06-23 12:13 ` Michal Hocko [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170623121342.GT5308@dhcp22.suse.cz \
--to=mhocko@suse.com \
--cc=akpm@linux-foundation.org \
--cc=bigeasy@linutronix.de \
--cc=linux-mm@kvack.org \
--cc=tglx@linutronix.de \
--cc=tim.c.chen@linux.intel.com \
--cc=ying.huang@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox