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From: Peter Zijlstra <peterz@infradead.org>
To: Dmitry Safonov <dima@arista.com>
Cc: linux-kernel@vger.kernel.org,
	"Dmitry Safonov" <0x7f454c46@gmail.com>,
	"Daniel Axtens" <dja@axtens.net>,
	"Dmitry Vyukov" <dvyukov@google.com>,
	"Michael Neuling" <mikey@neuling.org>,
	"Mikulas Patocka" <mpatocka@redhat.com>,
	"Nathan March" <nathan@gt.net>, "Pasi Kärkkäinen" <pasik@iki.fi>,
	"Peter Hurley" <peter@hurleysoftware.com>,
	"Rong, Chen" <rong.a.chen@intel.com>,
	"Sergey Senozhatsky" <sergey.senozhatsky.work@gmail.com>,
	"Tan Xiaojun" <tanxiaojun@huawei.com>,
	"Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Jiri Slaby" <jslaby@suse.com>
Subject: Re: [PATCHv3 6/6] tty/ldsem: Decrement wait_readers on timeouted down_read()
Date: Tue, 11 Sep 2018 15:50:04 +0200	[thread overview]
Message-ID: <20180911135004.GU24106@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1536672802.2710.33.camel@arista.com>

On Tue, Sep 11, 2018 at 02:33:22PM +0100, Dmitry Safonov wrote:
> > > You might want to think about ditching that ldsem thing entirely,
> > > and use a regular rwsem ?
> > 
> > Yeah, but AFAICS, regular rwsem will need to have a timeout then (for
> > write). So, I thought fixing this pile would be simpler than adding
> > timeout and probably writer-priority to generic rwsem?
> > 
> > And I guess, we still will need fixes for stable for the bugs here..
> > 
> > I expect that timeouts are ABI, while the gain of adding priority may
> > be measured. I'll give it a shot (adding timeout/priority for linux-
> > next) to rwsem if you say it's acceptable.
> 
> Actually, priority looks quite simple: we can add writers in the head
> of wait_list and it probably may work.
> Timeout looks also not a rocket science.
> So, I can try to do that if you say it's acceptable (with the gain
> measures).

So why do you need writer priority? The comment that goes with ldsems
doesn't explain I think, it just says it has it.

In general I dislike unfair locks, they always cause trouble.

> After this can of worms that I need to fix regardless.

Sure.

  reply	other threads:[~2018-09-11 13:50 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-11  1:48 [PATCHv3 0/6] tty: Hold write ldisc sem in tty_reopen() Dmitry Safonov
2018-09-11  1:48 ` [PATCHv3 1/6] tty: Drop tty->count on tty_reopen() failure Dmitry Safonov
2018-09-11  1:48 ` [PATCHv3 2/6] tty/ldsem: Update waiter->task before waking up reader Dmitry Safonov
2018-09-11  5:04   ` Sergey Senozhatsky
2018-09-11  5:41     ` Sergey Senozhatsky
2018-09-11 11:04       ` Kirill Tkhai
2018-09-11 11:44       ` Peter Zijlstra
2018-09-11 11:43     ` Peter Zijlstra
2018-09-11 11:40   ` Peter Zijlstra
2018-09-11 12:48     ` Dmitry Safonov
2018-09-11  1:48 ` [PATCHv3 3/6] tty: Hold tty_ldisc_lock() during tty_reopen() Dmitry Safonov
2018-09-11  1:48 ` [PATCHv3 4/6] tty/lockdep: Add ldisc_sem asserts Dmitry Safonov
2018-09-11 11:59   ` Peter Zijlstra
2018-09-11 12:01   ` Peter Zijlstra
2018-09-11 12:53     ` Dmitry Safonov
2018-09-11  1:48 ` [PATCHv3 5/6] tty: Simplify tty->count math in tty_reopen() Dmitry Safonov
2018-09-11  1:48 ` [PATCHv3 6/6] tty/ldsem: Decrement wait_readers on timeouted down_read() Dmitry Safonov
2018-09-11 12:02   ` Peter Zijlstra
2018-09-11 13:01     ` Dmitry Safonov
2018-09-11 13:33       ` Dmitry Safonov
2018-09-11 13:50         ` Peter Zijlstra [this message]
2018-09-11 15:04           ` Dmitry Safonov
2018-09-11 12:16 ` [PATCHv3 0/6] tty: Hold write ldisc sem in tty_reopen() Mark Rutland
2018-09-11 12:42   ` Dmitry Safonov

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