Re: [PATCH] drm/amdgpu: fix sleeping allocation under spinlock in PASID IDR

["Lazar, Lijo" <lijo.lazar@amd.com>]

On 29-Mar-26 3:09 AM, Mikhail Gavrilov wrote:
> Commit 14b81abe7bdc ("drm/amdgpu: prevent immediate PASID reuse case")
> switched from ida to idr_alloc_cyclic() protected by a spinlock, but
> passes GFP_KERNEL to the allocator.  idr_alloc_cyclic() may need to
> allocate radix-tree nodes, which with GFP_KERNEL can sleep — illegal
> under a spinlock that disables preemption.  With CONFIG_PREEMPT or
> lockdep enabled this triggers:
> 
>    BUG: sleeping function called from invalid context at
>         ./include/linux/sched/mm.h:323
>    in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 570
>    ...
>    #1: ffffffffc2cd24f8 (amdgpu_pasid_idr_lock){+.+.}-{3:3},
>        at: amdgpu_pasid_alloc+0x24/0x210 [amdgpu]
>    ...
>    kmem_cache_alloc_noprof+0x41d/0x780
>    radix_tree_node_alloc.constprop.0+0x56/0x3a0
>    idr_get_free+0x330/0x830
>    idr_alloc_u32+0x14a/0x2e0
>    idr_alloc_cyclic+0xd3/0x1d0
>    amdgpu_pasid_alloc+0x51/0x210 [amdgpu]
> 
> A mutex is not an option because amdgpu_pasid_free() is reachable from
> dma-fence callbacks (amdgpu_pasid_free_cb) which may run in IRQ context.
> 
> Use idr_preload(GFP_KERNEL) before taking the spinlock to pre-allocate
> radix-tree nodes, then pass GFP_NOWAIT inside the critical section so
> the allocator draws from the preloaded pool and never sleeps.  This is
> the standard kernel pattern for IDR allocation under a spinlock.
> 
> Fixes: 14b81abe7bdc ("drm/amdgpu: prevent immediate PASID reuse case")
> Cc: stable@vger.kernel.org
> Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c
> index d88523568b62..515775eab2ef 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c
> @@ -67,10 +67,12 @@ int amdgpu_pasid_alloc(unsigned int bits)
>   	if (bits == 0)
>   		return -EINVAL;
>   
> +	idr_preload(GFP_KERNEL);

It's better/simpler to replace amdgpu_pasid_idr with xarray.

Thanks,
Lijo

>   	spin_lock(&amdgpu_pasid_idr_lock);
>   	pasid = idr_alloc_cyclic(&amdgpu_pasid_idr, NULL, 1,
> -				 1U << bits, GFP_KERNEL);
> +				 1U << bits, GFP_NOWAIT);
>   	spin_unlock(&amdgpu_pasid_idr_lock);
> +	idr_preload_end();
>   
>   	if (pasid >= 0)
>   		trace_amdgpu_pasid_allocated(pasid);