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[net,v2,1/3] net: support kmap_local forced debugging in skb_frag_foreach

Message ID 20210109221834.3459768-2-willemdebruijn.kernel@gmail.com (mailing list archive)
State Accepted
Commit 29766bcffad03da66892bef82674883e31f78fec
Delegated to: Netdev Maintainers
Headers show
Series skb frag: kmap_atomic fixes | expand

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Commit Message

Willem de Bruijn Jan. 9, 2021, 10:18 p.m. UTC 
From: Willem de Bruijn <willemb@google.com>

Skb frags may be backed by highmem and/or compound pages. Highmem
pages need kmap_atomic mappings to access. But kmap_atomic maps a
single page, not the entire compound page.

skb_foreach_page iterates over an skb frag, in one step in the common
case, page by page only if kmap_atomic must be called for each page.
The decision logic is captured in skb_frag_must_loop.

CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP extends kmap from highmem to all
pages, to increase code coverage.

Extend skb_frag_must_loop to this new condition.

Link: https://lore.kernel.org/linux-mm/20210106180132.41dc249d@gandalf.local.home/
Fixes: 0e91a0c6984c ("mm/highmem: Provide CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP")
Reported-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/skbuff.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 333bcdc39635..c858adfb5a82 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -366,7 +366,7 @@  static inline void skb_frag_size_sub(skb_frag_t *frag, int delta)
 static inline bool skb_frag_must_loop(struct page *p)
 {
 #if defined(CONFIG_HIGHMEM)
-	if (PageHighMem(p))
+	if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP) || PageHighMem(p))
 		return true;
 #endif
 	return false;