RE: 3.7 RC1

From: KY Srinivasan
Date: Tue Oct 23 2012 - 10:25:32 EST

> -----Original Message-----
> From: Dan Carpenter [mailto:dan.carpenter@xxxxxxxxxx]
> Sent: Tuesday, October 23, 2012 1:47 AM
> To: KY Srinivasan
> Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx;
> jasowang@xxxxxxxxxx
> Subject: Re: 3.7 RC1
> On Mon, Oct 22, 2012 at 04:37:45PM -0700, K. Y. Srinivasan wrote:
> >
> > While testing 3.7 RC1 I discovered that invoking the function
> orderly_poweroff()
> > from an interrupt context will trigger an ASSERT(). This was not the case till
> > recently. The comment preceding the orderly_poweroff() function claims that
> this
> > function can be invoked from any context and in the current Hyper-V util driver,
> > we support host-driven orderly shut down of the guest by invoking this
> > orderly_poweroff() function in the context of the message callback. This code
> has
> > been working for a very long time and it is broken now. Is my assumption that
> > orderly_poweroff() could be invoked from the interrupt context a wrong
> assumption?
> You can't call orderly_poweroff() from interrupt context.

Thanks Dan; I am curious to understand the basis for your assertion.
As I noted earlier the documentation for this function clearly says it can
be called from any context. Furthermore, __orderly_poweroff(), the helper
function allocates memory with the GFP_ATOMIC flag set. Lastly, the behavior
of orderly_poweroff() has been such that this function could be called from interrupt context
for a very long time and something has changed now. For what it is worth, there are other users in
the kernel (in 3.7 RC1) that are invoking the orderly_poweroff() function from interrupt
context other than the Hyper-V shutdown handler: fsl_hv_shutdown_isr() in drivers/virt/fsl_hypervisor.c.
I suspect there are other users as well that have made this similar assumption.


K. Y

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