linux-kernel - [PATCH] lib/test_hmm.c: handle src_pfns and dst

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Message-Id: <20240312005905.9939-1-duoming@zju.edu.cn>
Date: Tue, 12 Mar 2024 08:59:05 +0800
From: Duoming Zhou <duoming@....edu.cn>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
	jglisse@...hat.com,
	akpm@...ux-foundation.org,
	Duoming Zhou <duoming@....edu.cn>
Subject: [PATCH] lib/test_hmm.c: handle src_pfns and dst_pfns allocation failure

The kcalloc() in dmirror_device_evict_chunk() will return null if
the physical memory has run out. As a result, if src_pfns or dst_pfns
is dereferenced, the null pointer dereference bug will happen.

Moreover, the device is going away. If the kcalloc() fails, the pages
mapping a chunk could not be evicted. So add a __GFP_NOFAIL flag in
kcalloc().

Finally, as there is no need to have physically contiguous memory,
Switch kcalloc() to kvcalloc() in order to avoid failing allocations.

Fixes: b2ef9f5a5cb3 ("mm/hmm/test: add selftest driver for HMM")
Signed-off-by: Duoming Zhou <duoming@....edu.cn>
---
 lib/test_hmm.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 717dcb83012..b823ba7cb6a 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -1226,8 +1226,8 @@ static void dmirror_device_evict_chunk(struct dmirror_chunk *chunk)
 	unsigned long *src_pfns;
 	unsigned long *dst_pfns;
 
-	src_pfns = kcalloc(npages, sizeof(*src_pfns), GFP_KERNEL);
-	dst_pfns = kcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL);
+	src_pfns = kvcalloc(npages, sizeof(*src_pfns), GFP_KERNEL | __GFP_NOFAIL);
+	dst_pfns = kvcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL | __GFP_NOFAIL);
 
 	migrate_device_range(src_pfns, start_pfn, npages);
 	for (i = 0; i < npages; i++) {
@@ -1250,8 +1250,8 @@ static void dmirror_device_evict_chunk(struct dmirror_chunk *chunk)
 	}
 	migrate_device_pages(src_pfns, dst_pfns, npages);
 	migrate_device_finalize(src_pfns, dst_pfns, npages);
-	kfree(src_pfns);
-	kfree(dst_pfns);
+	kvfree(src_pfns);
+	kvfree(dst_pfns);
 }
 
 /* Removes free pages from the free list so they can't be re-allocated */
-- 
2.17.1