Re: [PATCH v6 01/13] dma-buf: introduce initial file I/O infrastructure

[Pavel Begunkov <asml.silence@gmail.com>]

On 9/21/26 14:53, sashiko-bot@kernel.org wrote:
...>>   }
> [ ... ]
>> +int dma_buf_io_init_map(struct dma_buf_io_ctx *ctx, struct dma_buf_io_map *map,
>> +			struct sg_table *sgt)
>> +{
>> +	unsigned seg_shift = ~0U;
>> +	struct scatterlist *sg;
>> +	unsigned long tmp;
>> +	int ret;
>> +
>> +	for_each_sgtable_dma_sg(sgt, sg, tmp)
>> +		seg_shift = min(seg_shift, __ffs(sg_dma_len(sg)));
>> +
>> +	ret = percpu_ref_init(&map->refs, dma_buf_io_map_refs_release, 0,
>> +			      GFP_KERNEL);
> 
> [Severity: High]
> Does this GFP_KERNEL allocation violate DMA-buf locking rules?
> 
> dma_buf_io_create_map() calls ctx->dev_ops->map(ctx) while holding the
> dmabuf->resv ww_mutex. If the driver then calls dma_buf_io_init_map() under
> this lock, the GFP_KERNEL allocation could deadlock if memory reclaim
> attempts to acquire dma_resv locks.

Most of these look trivial, going to fix them. This one, however,
doesn't sound true AFAIU, I haven't heard about any blank ban on
GFP_KERNEL allocation under resv lock.

-- 
Pavel Begunkov