From: Michael Kelley <mhklinux@xxxxxxxxxxx> 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/SN6PR02MB4157210CC36B2593F8572E5ED4692@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ Signed-off-by: Michael Kelley <mhklinux@xxxxxxxxxxx> --- 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
