From: Andrea Arcangeli <andrea@suse.de>
To: Jari Ruusu <jari.ruusu@pp.inet.fi>
Cc: Jens Axboe <axboe@suse.de>,
Marcelo Tosatti <marcelo@conectiva.com.br>,
Herbert Valerio Riedel <hvr@hvrlab.org>,
linux-kernel@vger.kernel.org
Subject: Re: 2.4.19pre3aa2
Date: Fri, 15 Mar 2002 18:57:47 +0100 [thread overview]
Message-ID: <20020315185747.P10073@dualathlon.random> (raw)
In-Reply-To: <20020314032801.C1273@dualathlon.random> <3C912ACF.AF3EE6F0@pp.inet.fi> <20020315105621.GA22169@suse.de> <3C9230C6.4119CB4C@pp.inet.fi>
In-Reply-To: <3C9230C6.4119CB4C@pp.inet.fi>
On Fri, Mar 15, 2002 at 07:35:02PM +0200, Jari Ruusu wrote:
> Jens Axboe wrote:
> > On Fri, Mar 15 2002, Jari Ruusu wrote:
> > > - No more illegal sleeping in generic_make_request().
> >
> > I've told you this before -- sleeping in make_request is not illegal,
> > heck it happens _all the time_. Safely sleeping requires a reserved pool
> > of the units you wish to allocate, of course. In fact I think that would
> > be much nicer than the path you are following here by delaying
> > allocations to the loop thread (and still not using a reserved pool).
>
> Yes, I know you have told me that before, but I'm being overcareful. See:
>
> <quote> from device drivers book by Alessandro Rubini, chapter 12, page 331
> The request function has one very important constraint: it must be atomic.
> request is not usually called in direct response to user requests, and it is
> not running in the context of any particular process. It can be called at
> interrupt time, from tasklets, or from any number of other places. Thus, it
> must not sleep while carrying out its tasks.
> </quote>
loop isn't implement via ->request_fn anymore. Loop since 2.4 is only
driven by the ->make_request_fn, that for the other more normal devices
just means the old legacy __make_request. request_fn is subject to the
rules pointed out by Alessandro, but ->make_request_fn can sleep just
like ll_rw_block can sleep. ->make_request_fn and in turn
loop_make_request can only run in normal context with irq enabled and
they're both allowed to sleep just like ll_rw_block and submit_bh.
Nevertheless as Jens said the infinite-loop-allocation in the
->make_request_fn path are deadlock prone at the moment, not because
they sleeps but because they need a reserved mempool to guarantee
operations can go ahead slowly without deadlocks even if dynamic
allocation fails, but this is not a very pratical problem, it's very
unlikely to deadlock there (it's not worse than the other infinite loop
in getblk() that affects not just loop).
Andrea
next prev parent reply other threads:[~2002-03-15 17:57 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-03-14 2:28 2.4.19pre3aa2 Andrea Arcangeli
2002-03-14 12:32 ` 2.4.19pre3aa2 Dave Jones
2002-03-14 12:37 ` 2.4.19pre3aa2 Andrea Arcangeli
2002-03-14 12:46 ` 2.4.19pre3aa2 Jeff Garzik
2002-03-14 12:59 ` 2.4.19pre3aa2 Dave Jones
2002-03-14 15:53 ` 2.4.19pre3aa2 Bill Davidsen
2002-03-14 16:12 ` 2.4.19pre3aa2 Andrea Arcangeli
2002-03-14 16:16 ` 2.4.19pre3aa2 Dave Jones
2002-03-14 16:32 ` 2.4.19pre3aa2 Andrea Arcangeli
2002-03-16 1:26 ` 2.4.19pre3aa2 Mike Fedyk
2002-03-14 16:13 ` 2.4.19pre3aa2 Dave Jones
2002-03-14 17:16 ` 2.4.19pre3aa2 Bill Davidsen
2002-03-14 21:16 ` 2.4.19pre3aa2 H. Peter Anvin
2002-03-14 18:00 ` 2.4.19pre3aa2 Andrew Morton
2002-03-14 22:57 ` 2.4.19pre3aa2 Jari Ruusu
2002-03-15 10:56 ` 2.4.19pre3aa2 Jens Axboe
2002-03-15 11:06 ` 2.4.19pre3aa2 Jens Axboe
2002-03-15 17:35 ` 2.4.19pre3aa2 Jari Ruusu
2002-03-15 17:57 ` Andrea Arcangeli [this message]
2002-03-16 12:10 ` 2.4.19pre3aa2 Jari Ruusu
2002-03-16 13:54 ` 2.4.19pre3aa2 Andrea Arcangeli
2002-03-18 19:13 ` 2.4.19pre3aa2 Jens Axboe
2002-03-19 23:26 ` 2.4.19pre3aa2 Jari Ruusu
2002-03-20 7:54 ` 2.4.19pre3aa2 Jens Axboe
2002-03-20 18:16 ` 2.4.19pre3aa2 Jari Ruusu
2002-03-20 14:21 ` 2.4.19pre3aa2 Herbert Valerio Riedel
2002-03-15 12:19 ` 2.4.19pre3aa2 Herbert Valerio Riedel
2002-03-15 17:36 ` 2.4.19pre3aa2 Jari Ruusu
2002-03-15 18:36 ` 2.4.19pre3aa2 Herbert Valerio Riedel
2002-03-16 12:12 ` 2.4.19pre3aa2 Jari Ruusu
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