[RESEND, v3] cxl: Prevent adapter reset if an active context exists

[Michael Ellerman]

On Fri, 2016-14-10 at 09:38:36 UTC, Vaibhav Jain wrote:
> This patch prevents resetting the cxl adapter via sysfs in presence of
> one or more active cxl_context on it. This protects against an
> unrecoverable error caused by PSL owning a dirty cache line even after
> reset and host tries to touch the same cache line. In case a force reset
> of the card is required irrespective of any active contexts, the int
> value -1 can be stored in the 'reset' sysfs attribute of the card.
> 
> The patch introduces a new atomic_t member named contexts_num inside
> struct cxl that holds the number of active context attached to the card
> , which is checked against '0' before proceeding with the reset. To
> prevent against a race condition where a context is activated just after
> reset check is performed, the contexts_num is atomically set to '-1'
> after reset-check to indicate that no more contexts can be activated on
> the card anymore.
> 
> Before activating a context we atomically test if contexts_num is
> non-negative and if so, increment its value by one. In case the value of
> contexts_num is negative then it indicates that the card is about to be
> reset and context activation is error-ed out at that point.
> 
> Cc: stable at vger.kernel.org
> Fixes: 62fa19d4 ("cxl: Add ability to reset the card")
> Acked-by: Frederic Barrat <fbarrat at linux.vnet.ibm.com>
> Reviewed-by: Andrew Donnellan <andrew.donnellan at au1.ibm.com>
> Signed-off-by: Vaibhav Jain <vaibhav at linux.vnet.ibm.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/70b565bbdb911023373e035225ab10

cheers