* Re: [PATCH v3] dma/pool: distinguish between missing and exhausted atomic pools
2026-01-28 13:35 ` [PATCH v3] dma/pool: distinguish between missing and exhausted atomic pools Sai Sree Kartheek Adivi
@ 2026-01-28 14:05 ` Robin Murphy
2026-01-29 9:26 ` Marek Szyprowski
1 sibling, 0 replies; 3+ messages in thread
From: Robin Murphy @ 2026-01-28 14:05 UTC (permalink / raw)
To: Sai Sree Kartheek Adivi, m.szyprowski, iommu, linux-kernel; +Cc: vigneshr
On 2026-01-28 1:35 pm, Sai Sree Kartheek Adivi wrote:
> Currently, dma_alloc_from_pool() unconditionally warns and dumps a stack
> trace when an allocation fails, with the message "Failed to get suitable
> pool".
>
> This conflates two distinct failure modes:
> 1. Configuration error: No atomic pool is available for the requested
> DMA mask (a fundamental system setup issue)
> 2. Resource Exhaustion: A suitable pool exists but is currently full (a
> recoverable runtime state)
>
> This lack of distinction prevents drivers from using __GFP_NOWARN to
> suppress error messages during temporary pressure spikes, such as when
> awaiting synchronous reclaim of descriptors.
>
> Refactor the error handling to distinguish these cases:
> - If no suitable pool is found, keep the unconditional WARN regarding
> the missing pool.
> - If a pool was found but is exhausted, respect __GFP_NOWARN and update
> the warning message to explicitly state "DMA pool exhausted".
Great writeup!
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
> Fixes: 9420139f516d ("dma-pool: fix coherent pool allocations for IOMMU mappings")
> Signed-off-by: Sai Sree Kartheek Adivi <s-adivi@ti.com>
> ---
>
> Changes from v2 to v3:
> - Distinguish between "no suitable pool is found" and "pool is
> exhausted" cases.
> Link: https://lore.kernel.org/all/20260112104749.4132641-1-s-adivi@ti.com/
>
> kernel/dma/pool.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> index c5da29ad010c4..2b2fbb7092429 100644
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -277,15 +277,20 @@ struct page *dma_alloc_from_pool(struct device *dev, size_t size,
> {
> struct gen_pool *pool = NULL;
> struct page *page;
> + bool pool_found = false;
>
> while ((pool = dma_guess_pool(pool, gfp))) {
> + pool_found = true;
> page = __dma_alloc_from_pool(dev, size, pool, cpu_addr,
> phys_addr_ok);
> if (page)
> return page;
> }
>
> - WARN(1, "Failed to get suitable pool for %s\n", dev_name(dev));
> + if (pool_found)
> + WARN(!(gfp & __GFP_NOWARN), "DMA pool exhausted for %s\n", dev_name(dev));
> + else
> + WARN(1, "Failed to get suitable pool for %s\n", dev_name(dev));
> return NULL;
> }
>
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH v3] dma/pool: distinguish between missing and exhausted atomic pools
2026-01-28 13:35 ` [PATCH v3] dma/pool: distinguish between missing and exhausted atomic pools Sai Sree Kartheek Adivi
2026-01-28 14:05 ` Robin Murphy
@ 2026-01-29 9:26 ` Marek Szyprowski
1 sibling, 0 replies; 3+ messages in thread
From: Marek Szyprowski @ 2026-01-29 9:26 UTC (permalink / raw)
To: Sai Sree Kartheek Adivi, robin.murphy, iommu, linux-kernel; +Cc: vigneshr
On 28.01.2026 14:35, Sai Sree Kartheek Adivi wrote:
> Currently, dma_alloc_from_pool() unconditionally warns and dumps a stack
> trace when an allocation fails, with the message "Failed to get suitable
> pool".
>
> This conflates two distinct failure modes:
> 1. Configuration error: No atomic pool is available for the requested
> DMA mask (a fundamental system setup issue)
> 2. Resource Exhaustion: A suitable pool exists but is currently full (a
> recoverable runtime state)
>
> This lack of distinction prevents drivers from using __GFP_NOWARN to
> suppress error messages during temporary pressure spikes, such as when
> awaiting synchronous reclaim of descriptors.
>
> Refactor the error handling to distinguish these cases:
> - If no suitable pool is found, keep the unconditional WARN regarding
> the missing pool.
> - If a pool was found but is exhausted, respect __GFP_NOWARN and update
> the warning message to explicitly state "DMA pool exhausted".
>
> Fixes: 9420139f516d ("dma-pool: fix coherent pool allocations for IOMMU mappings")
> Signed-off-by: Sai Sree Kartheek Adivi <s-adivi@ti.com>
Applied to dma-mapping-fixes. Thanks!
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
^ permalink raw reply [flat|nested] 3+ messages in thread