[PATCH] ocxl: Fix concurrent AFU open and device removal

[Michael Ellerman]

On Mon, 2019-06-24 at 14:41:48 UTC, Frederic Barrat wrote:
> If an ocxl device is unbound through sysfs at the same time its AFU is
> being opened by a user process, the open code may dereference freed
> stuctures, which can lead to kernel oops messages. You'd have to hit a
> tiny time window, but it's possible. It's fairly easy to test by
> making the time window bigger artificially.
> 
> Fix it with a combination of 2 changes:
> - when an AFU device is found in the IDR by looking for the device
> minor number, we should hold a reference on the device until after the
> context is allocated. A reference on the AFU structure is kept when
> the context is allocated, so we can release the reference on the
> device after the context allocation.
> - with the fix above, there's still another even tinier window,
> between the time the AFU device is found in the IDR and the reference
> on the device is taken. We can fix this one by removing the IDR entry
> earlier, when the device setup is removed, instead of waiting for the
> 'release' device callback. With proper locking around the IDR.
> 
> Fixes: 75ca758adbaf ("ocxl: Create a clear delineation between ocxl backend & frontend")
> Signed-off-by: Frederic Barrat <fbarrat at linux.ibm.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/a58d37bce0d21cf7fbd589384c619e465ef2f927

cheers