Re: [PATCH] drm/panthor: Fix potential memleak of vma structure

[Boris Brezillon <boris.brezillon@collabora.com>]

On Mon, 20 Oct 2025 10:50:19 +0100
Akash Goel <akash.goel@arm.com> wrote:

> On 10/20/25 10:30, Boris Brezillon wrote:
> > On Mon, 20 Oct 2025 09:59:14 +0100
> > Akash Goel <akash.goel@arm.com> wrote:
> >   
> >> This commit addresses a memleak issue of panthor_vma (or drm_gpuva)
> >> structure in Panthor driver, that can happen if the GPU page table
> >> update operation to map the pages fail.
> >> The issue is very unlikely to occur in practice.
> >>
> >> Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
> >> Signed-off-by: Akash Goel <akash.goel@arm.com>
> >> ---
> >>   drivers/gpu/drm/panthor/panthor_mmu.c | 4 +++-
> >>   1 file changed, 3 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> >> index 6dec4354e378..34a86f7b58d9 100644
> >> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> >> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> >> @@ -2081,8 +2081,10 @@ static int panthor_gpuva_sm_step_map(struct drm_gpuva_op *op, void *priv)
> >>   	ret = panthor_vm_map_pages(vm, op->map.va.addr, flags_to_prot(vma->flags),
> >>   				   op_ctx->map.sgt, op->map.gem.offset,
> >>   				   op->map.va.range);
> >> -	if (ret)
> >> +	if (ret) {
> >> +		kfree(vma);  
> > 
> > Calling kfree() in this context is probably fine, but I think I'd
> > prefer if we were introducing a panthor_vm_op_ctx_return_vma() helper
> > returning the vma to the preallocated array, and letting the deferred
> > cleanup function free this up.  
> 
> 
> Thanks for the quick review.
> 
> So need to do like this, where we search for a NULL entry to store the 
> VMA pointer to be returned ?
> 
> static void
> panthor_vm_op_ctx_return_vma(struct panthor_vm_op_ctx *op_ctx,
> 			     struct panthor_vma *vma)
> {
> 	for (u32 i = 0; i < ARRAY_SIZE(op_ctx->preallocated_vmas); i++) {
> 		if (!op_ctx->preallocated_vmas[i]) {
> 			op_ctx->preallocated_vmas[i] = vma;
> 			return;
> 		}
> 	}
> }
> 
> 
> Please let me know.

Yep, that looks good to me.