From: "David McIlwraith" <quack@bigpond.net.au>
To: "Martin Diehl" <lists@mdiehl.de>
Cc: <linux-kernel@vger.kernel.org>
Subject: Re: calling context when writing to tty_driver
Date: Tue, 1 Oct 2002 21:13:22 +1000 [thread overview]
Message-ID: <08e001c2693b$8e64e8c0$41368490@archaic> (raw)
In-Reply-To: Pine.LNX.4.21.0210010523290.485-100000@notebook.diehl.home
Semaphores may sleep - therefore, they cannot be used from a 'non-sleep'
context.
Sincerely,
David McIlwraith quack@bigpond.net.au
----- Original Message -----
From: "Martin Diehl" <lists@mdiehl.de>
To: <linux-kernel@vger.kernel.org>
Cc: "Greg KH" <greg@kroah.com>
Sent: Tuesday, October 01, 2002 8:37 PM
Subject: calling context when writing to tty_driver
>
> Hi,
>
> just hitting another "sleeping on semaphore from illegal context" issue
> with 2.5.39. Happened on down() in either usbserial->write_room() or
> usbserial->write(), when invoked from bh context.
>
> Some grepping reveals no documentation of calling context requirements
> for those driver calls and existing serial code seems to be happy with bh
> context. Therefore I'm wondering whether it is permitted to call from
> don't-sleep context?
>
> Since write_room() is usually called immediately before write()'ing stuff
> to the driver it would be a good idea to keep them both callable from bh,
> IMHO. For example tty_ldisc->write_wakeup() might probably want to issue
> write_room() followed by write().
>
> Currently, usbserial calls write_wakeup() from bh (on OUT urb completion)
> but needs process context for write_room() and write(). My impression is
> the whole point of write_room() is to find out how many data can be
> accepted by the write() - if write() would be allowed to sleep it could
> just block to deal with any amount of data.
>
> TIA for any insight.
>
> Martin
>
> -
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next prev parent reply other threads:[~2002-10-01 11:08 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-10-01 10:37 calling context when writing to tty_driver Martin Diehl
2002-10-01 11:13 ` David McIlwraith [this message]
2002-10-01 11:28 ` Martin Diehl
2002-10-01 11:32 ` David McIlwraith
2002-10-01 18:34 ` Greg KH
2002-10-01 19:30 ` Russell King
2002-10-01 21:10 ` Martin Diehl
2002-10-03 6:52 ` Greg KH
2002-10-03 9:51 ` Paul Mackerras
2002-10-03 21:36 ` Martin Diehl
2002-10-01 23:20 ` Paul Mackerras
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