Patch "powerpc/xive: Fix the size of the cpumask used in xive_find_target_in_mask()" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/xive: Fix the size of the cpumask used in xive_find_target_in_mask()

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-xive-fix-the-size-of-the-cpumask-used-in-xive_find_target_in_mask.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= <[email protected]>
Date: Tue, 8 Aug 2017 11:02:49 +0200
Subject: powerpc/xive: Fix the size of the cpumask used in xive_find_target_in_mask()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Cédric Le Goater <[email protected]>

commit a9dadc1c512807f955f0799e85830b420da47932 upstream.

When called from xive_irq_startup(), the size of the cpumask can be larger than nr_cpu_ids. This can result in a WARN_ON such as:

  WARNING: CPU: 10 PID: 1 at ../arch/powerpc/sysdev/xive/common.c:476 xive_find_target_in_mask+0x110/0x2f0
  ...
  NIP [c00000000008a310] xive_find_target_in_mask+0x110/0x2f0
  LR [c00000000008a2e4] xive_find_target_in_mask+0xe4/0x2f0
  Call Trace:
    xive_find_target_in_mask+0x74/0x2f0 (unreliable)
    xive_pick_irq_target.isra.1+0x200/0x230
    xive_irq_startup+0x60/0x180
    irq_startup+0x70/0xd0
    __setup_irq+0x7bc/0x880
    request_threaded_irq+0x14c/0x2c0
    request_event_sources_irqs+0x100/0x180
    __machine_initcall_pseries_init_ras_IRQ+0x104/0x134
    do_one_initcall+0x68/0x1d0
    kernel_init_freeable+0x290/0x374
    kernel_init+0x24/0x170
    ret_from_kernel_thread+0x5c/0x74

This happens because we're being called with our affinity mask set to irq_default_affinity. That in turn was populated using cpumask_setall(), which sets NR_CPUs worth of bits, not nr_cpu_ids worth. Finally cpumask_weight() will return > nr_cpu_ids when passed a mask which has > nr_cpu_ids bits set.

Fix it by limiting the value returned by cpumask_weight().

---
 arch/powerpc/sysdev/xive/common.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -447,7 +447,7 @@ static int xive_find_target_in_mask(cons
 	int cpu, first, num, i;
 
 	/* Pick up a starting point CPU in the mask based on  fuzz */
-	num = cpumask_weight(mask);
+	num = min_t(int, cpumask_weight(mask), nr_cpu_ids);
 	first = fuzz % num;
 
 	/* Locate it */

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/powerpc-xive-fix-the-size-of-the-cpumask-used-in-xive_find_target_in_mask.patch