From: Michael Kelley <mhkli...@outlook.com>

Current code allocates the stor_chns array with size num_possible_cpus().
This code assumes cpu_possible_mask is dense, which is not true in
the general case per [1]. If cpu_possible_mask is sparse, the array
might be indexed by a value beyond the size of the array.

However, the configurations that Hyper-V provides to guest VMs on x86
and ARM64 hardware, in combination with how architecture specific code
assigns Linux CPU numbers, *does* always produce a dense cpu_possible_mask.
So the dense assumption is not currently causing failures. But for
robustness against future changes in how cpu_possible_mask is populated,
update the code to no longer assume dense.

The correct approach is to allocate and initialize the array using size
"nr_cpu_ids". While this leaves unused array entries corresponding to
holes in cpu_possible_mask, the holes are assumed to be minimal and hence
the amount of memory wasted by unused entries is minimal.

[1] 
https://lore.kernel.org/lkml/sn6pr02mb4157210cc36b2593f8572e5ed4...@sn6pr02mb4157.namprd02.prod.outlook.com/

Signed-off-by: Michael Kelley <mhkli...@outlook.com>
---
 drivers/scsi/storvsc_drv.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 11b3fc3b24c9..f2beb6b23284 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -917,14 +917,13 @@ static int storvsc_channel_init(struct hv_device *device, 
bool is_fc)
 
        /*
         * Allocate state to manage the sub-channels.
-        * We allocate an array based on the numbers of possible CPUs
-        * (Hyper-V does not support cpu online/offline).
-        * This Array will be sparseley populated with unique
-        * channels - primary + sub-channels.
-        * We will however populate all the slots to evenly distribute
-        * the load.
+        * We allocate an array based on the number of CPU ids. This array
+        * is initially sparsely populated for the CPUs assigned to channels:
+        * primary + sub-channels. As I/Os are initiated by different CPUs,
+        * the slots for all online CPUs are populated to evenly distribute
+        * the load across all channels.
         */
-       stor_device->stor_chns = kcalloc(num_possible_cpus(), sizeof(void *),
+       stor_device->stor_chns = kcalloc(nr_cpu_ids, sizeof(void *),
                                         GFP_KERNEL);
        if (stor_device->stor_chns == NULL)
                return -ENOMEM;
-- 
2.25.1


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