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From: "David McIlwraith" <>
To: "Martin Diehl" <>
Cc: <>
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'

David McIlwraith

----- Original Message -----
From: "Martin Diehl" <>
To: <>
Cc: "Greg KH" <>
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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  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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