linux-kernel - Re: Why can't we sleep in an ISR?

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Date:	Mon, 14 May 2007 12:46:26 +0530
From:	"Learning Linux" <learninglinux4@...il.com>
To:	"pradeep singh" <2500.pradeep@...il.com>
Cc:	kernelnewbies@...linux.org, linux-newbie@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Why can't we sleep in an ISR?

> > I have a very basic doubt here ... what makes it impossible to sleep
> > in an ISR? I mean, I know that the kernel preemption is disabled and
> > the kernel will panic, but I could not understand why?
>
> Because the interrupt which you are serving in the
> ISR has been masked to avoid preemption(
> true for maskable inetrrupts ).Any locks you are holding in ISR are now with
> you solely. So, if you try to sleep you take the locks you untill you are
> rescheduled and complete. This may lead to
> a deadlock for the lock resource.

Ok, but how about an ISR, that does not take any locks? Why can't we
sleep in SUCH an ISR?

AFAIK, taking a lock disables kernel preemption, and hence it is not
allowed to sleep. So I think my question would boil down to why is
sleeping not allowed when the kernel preemption is disabled.

LL
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