Re: [PATCH v2 09/30] cxlflash: Fix to stop interrupt processing on remove

On Sep 17, 2015, at 6:58 AM, David Laight [off-list ref] =

wrote:

=20
From: Linuxppc-dev Matthew R. Ochs

quoted

Sent: 16 September 2015 22:28
Interrupt processing can run in parallel to a remove operation. This
can lead to a condition where the interrupt handler is processing =

with

quoted

memory that has been freed.
=20
To avoid processing an interrupt while memory may be yanked, check =

for

quoted

removal while in the interrupt handler. Bail when removal is =

imminent.

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On the face of it this just reduces the size of the window somewhat.

Agreed.

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What happens if the interrupt routine reads the flag just before it is =

set

(so is processing the entry that is being removed) and is then (say)
interrupted by a higher priority interrupt that takes longer to =

execute than

the remove code?

Understood. To completely close we'd need to either introduce a lock or =
a
reciprocal flag/count such that the remove doesn't make forward progress
until after interrupt processing has completed. I can look at =
introducing such
a mechanism in a later patch to fully remove the exposure.


-matt