From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH 6/6] sched: Change task_struct::state Date: Wed, 2 Jun 2021 10:06:58 -0400 (EDT) Message-ID: <896642516.5866.1622642818225.JavaMail.zimbra@efficios.com> References: <20210602131225.336600299@infradead.org> <20210602133040.587042016@infradead.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 79BFA302868 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1622642818; bh=GwH0GdcKUFmXjwdSc5PC6qayNfPYEbeSfo7iFd8LGlc=; h=Date:From:To:Message-ID:MIME-Version; b=IzY7rj9bG67qO5MhQCvNkTZ6NmKLl+j7CGAPSRZx3M3VXN4GE9cW/xiqKbb0lMrag set1cTsKpmrC3scRLhvadBwRFL0ucET03FgN+RYhAetywU7SMjz4Jzot43Al7b42/w wRf/j9ODOuM7qSvP03brlcfNA9m+dmMrwW5plmJFJwkQAs2hFyj/Dx0kstoADKFw0s PShGdCuiX9KikFibuSZcET8LNklvf4YN8WFNh0QHjOaoJ5JxioNYTizyl5WrJqstOz gIo6cZK3qsMar7jMzCrxaFOM5us8879gVttQyPgo4y+VuhrGp7sB3x4o9l+rwPGYzG yQHn8ljzHTpmw== In-Reply-To: <20210602133040.587042016-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> List-ID: Content-Type: text/plain; charset="us-ascii" To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , rostedt , Ben Segall , Mel Gorman , bristot , Borislav Petkov , x86 , "H. Peter Anvin" , Jens Axboe , Alasdair Kergon , Mike Snitzer , dm-devel , "David S. Miller" , Jakub Kicinski , Felipe Balbi , Greg Kroah-Hartman , Alexander Viro , Tejun Heo ----- On Jun 2, 2021, at 9:12 AM, Peter Zijlstra peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org wrote: > Change the type and name of task_struct::state. Drop the volatile and > shrink it to an 'unsigned int'. Rename it in order to find all uses > such that we can use READ_ONCE/WRITE_ONCE as appropriate. > [...] > > --- a/block/blk-mq.c > +++ b/block/blk-mq.c [...] > @@ -1559,7 +1560,8 @@ static int fill_psinfo(struct elf_prpsin > psinfo->pr_pgrp = task_pgrp_vnr(p); > psinfo->pr_sid = task_session_vnr(p); > > - i = p->state ? ffz(~p->state) + 1 : 0; > + state = READ_ONCE(p->__state); > + i = state ? ffz(~state) + 1 : 0; > psinfo->pr_state = i; > psinfo->pr_sname = (i > 5) ? '.' : "RSDTZW"[i]; > psinfo->pr_zomb = psinfo->pr_sname == 'Z'; [...] > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -113,13 +113,13 @@ struct task_group; > __TASK_TRACED | EXIT_DEAD | EXIT_ZOMBIE | \ > TASK_PARKED) > > -#define task_is_running(task) (READ_ONCE((task)->state) == TASK_RUNNING) > +#define task_is_running(task) (READ_ONCE((task)->__state) == TASK_RUNNING) > > -#define task_is_traced(task) ((task->state & __TASK_TRACED) != 0) > +#define task_is_traced(task) ((READ_ONCE(task->__state) & __TASK_TRACED) != 0) > > -#define task_is_stopped(task) ((task->state & __TASK_STOPPED) != 0) > +#define task_is_stopped(task) ((READ_ONCE(task->__state) & __TASK_STOPPED) != > 0) > > -#define task_is_stopped_or_traced(task) ((task->state & (__TASK_STOPPED | > __TASK_TRACED)) != 0) > +#define task_is_stopped_or_traced(task) ((READ_ONCE(task->__state) & > (__TASK_STOPPED | __TASK_TRACED)) != 0) > > #ifdef CONFIG_DEBUG_ATOMIC_SLEEP > > @@ -134,14 +134,14 @@ struct task_group; > do { \ > WARN_ON_ONCE(is_special_task_state(state_value));\ > current->task_state_change = _THIS_IP_; \ > - current->state = (state_value); \ > + WRITE_ONCE(current->__state, (state_value)); \ > } while (0) Why not introduce set_task_state(p) and get_task_state(p) rather than sprinkle READ_ONCE() and WRITE_ONCE() all over the kernel ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com