linux-kernel - [PATCH v3] dma/pool: distinguish between missing and exhausted atomic pools

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Message-ID: <20260128133554.3056582-1-s-adivi@ti.com>
Date: Wed, 28 Jan 2026 19:05:54 +0530
From: Sai Sree Kartheek Adivi <s-adivi@...com>
To: <m.szyprowski@...sung.com>, <robin.murphy@....com>,
	<iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
CC: <vigneshr@...com>
Subject: [PATCH v3] dma/pool: distinguish between missing and exhausted atomic pools

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@...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;
 }
 
-- 
2.34.1