Re: [PATCH] dmaengine: idxd: Fix oops during rmmod on single-CPU platforms

[Dave Jiang]

On 3/13/24 2:40 PM, Fenghua Yu wrote:
> During the removal of the idxd driver, registered offline callback is
> invoked as part of the clean up process. However, on systems with only
> one CPU online, no valid target is available to migrate the
> perf context, resulting in a kernel oops:
> 
>     BUG: unable to handle page fault for address: 000000000002a2b8
>     #PF: supervisor write access in kernel mode
>     #PF: error_code(0x0002) - not-present page
>     PGD 1470e1067 P4D 0 
>     Oops: 0002 [#1] PREEMPT SMP NOPTI
>     CPU: 0 PID: 20 Comm: cpuhp/0 Not tainted 6.8.0-rc6-dsa+ #57
>     Hardware name: Intel Corporation AvenueCity/AvenueCity, BIOS BHSDCRB1.86B.2492.D03.2307181620 07/18/2023
>     RIP: 0010:mutex_lock+0x2e/0x50
>     ...
>     Call Trace:
>     <TASK>
>     __die+0x24/0x70
>     page_fault_oops+0x82/0x160
>     do_user_addr_fault+0x65/0x6b0
>     __pfx___rdmsr_safe_on_cpu+0x10/0x10
>     exc_page_fault+0x7d/0x170
>     asm_exc_page_fault+0x26/0x30
>     mutex_lock+0x2e/0x50
>     mutex_lock+0x1e/0x50
>     perf_pmu_migrate_context+0x87/0x1f0
>     perf_event_cpu_offline+0x76/0x90 [idxd]
>     cpuhp_invoke_callback+0xa2/0x4f0
>     __pfx_perf_event_cpu_offline+0x10/0x10 [idxd]
>     cpuhp_thread_fun+0x98/0x150
>     smpboot_thread_fn+0x27/0x260
>     smpboot_thread_fn+0x1af/0x260
>     __pfx_smpboot_thread_fn+0x10/0x10
>     kthread+0x103/0x140
>     __pfx_kthread+0x10/0x10
>     ret_from_fork+0x31/0x50
>     __pfx_kthread+0x10/0x10
>     ret_from_fork_asm+0x1b/0x30
>     <TASK>
> 
> Fix the issue by preventing the migration of the perf context to an
> invalid target.
> 
> Fixes: 81dd4d4d6178 ("dmaengine: idxd: Add IDXD performance monitor support")
> Reported-by: Terrence Xu <terrence.xu@xxxxxxxxx>
> Tested-by: Terrence Xu <terrence.xu@xxxxxxxxx>
> Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>

Cc: Tom Zanussi


> ---
>  drivers/dma/idxd/perfmon.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/dma/idxd/perfmon.c b/drivers/dma/idxd/perfmon.c
> index fdda6d604262..5e94247e1ea7 100644
> --- a/drivers/dma/idxd/perfmon.c
> +++ b/drivers/dma/idxd/perfmon.c
> @@ -528,14 +528,11 @@ static int perf_event_cpu_offline(unsigned int cpu, struct hlist_node *node)
>  		return 0;
>  
>  	target = cpumask_any_but(cpu_online_mask, cpu);
> -
>  	/* migrate events if there is a valid target */
> -	if (target < nr_cpu_ids)
> +	if (target < nr_cpu_ids) {
>  		cpumask_set_cpu(target, &perfmon_dsa_cpu_mask);
> -	else
> -		target = -1;
> -
> -	perf_pmu_migrate_context(&idxd_pmu->pmu, cpu, target);
> +		perf_pmu_migrate_context(&idxd_pmu->pmu, cpu, target);
> +	}
>  
>  	return 0;
>  }