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From: David Rientjes <rientjes@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [patch] mm, thp: fix defrag setting if newline is not used
Date: Tue, 14 Jan 2020 17:58:36 -0800 (PST)	[thread overview]
Message-ID: <alpine.DEB.2.21.2001141757490.108121@chino.kir.corp.google.com> (raw)

If thp defrag setting "defer" is used and a newline is *not* used when
writing to the sysfs file, this is interpreted as the "defer+madvise"
option.

This is because we do prefix matching and if five characters are written
without a newline, the current code ends up comparing to the first five
bytes of the "defer+madvise" option and using that instead.

Find the length of what the user is writing and use that to guide our
decision on which string comparison to do.

Fixes: 21440d7eb904 ("mm, thp: add new defer+madvise defrag option")
Signed-off-by: David Rientjes <rientjes@google.com>
---
 This can be done in *many* different ways including extracting logic to
 a helper function.  If someone would like this to be implemented
 differently, please suggest it.

 mm/huge_memory.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -250,32 +250,33 @@ static ssize_t defrag_store(struct kobject *kobj,
 			    struct kobj_attribute *attr,
 			    const char *buf, size_t count)
 {
-	if (!memcmp("always", buf,
-		    min(sizeof("always")-1, count))) {
+	size_t len = count;
+
+	/* For prefix matching, find the length of interest */
+	if (buf[len-1] == '\n')
+		len--;
+
+	if (len == sizeof("always")-1 && !memcmp("always", buf, len)) {
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
 		set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
-	} else if (!memcmp("defer+madvise", buf,
-		    min(sizeof("defer+madvise")-1, count))) {
+	} else if (len == sizeof("defer+madvise")-1 && !memcmp("defer+madvise", buf, len)) {
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
 		set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
-	} else if (!memcmp("defer", buf,
-		    min(sizeof("defer")-1, count))) {
+	} else if (len == sizeof("defer")-1 && !memcmp("defer", buf, len)) {
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
 		set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
-	} else if (!memcmp("madvise", buf,
-			   min(sizeof("madvise")-1, count))) {
+	} else if (len == sizeof("madvise")-1 && !memcmp("madvise", buf, len)) {
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
 		set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
-	} else if (!memcmp("never", buf,
-			   min(sizeof("never")-1, count))) {
+	} else if (len == sizeof("never")-1 && !memcmp("never", buf, len)) {
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
 		clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);

             reply	other threads:[~2020-01-15  1:58 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-15  1:58 David Rientjes [this message]
2020-01-15  1:58 ` [patch] mm, thp: fix defrag setting if newline is not used David Rientjes
2020-01-15 12:45 ` Vlastimil Babka
2020-01-17  3:16 ` Andrew Morton
2020-01-17  8:24   ` Vlastimil Babka
2020-01-17  9:43     ` David Rientjes
2020-01-17  9:43       ` David Rientjes
2020-01-17 10:12       ` Vlastimil Babka
2020-01-17 22:11         ` [patch v2] " David Rientjes
2020-01-17 22:11           ` David Rientjes
2020-01-18 10:54           ` Vlastimil Babka
2020-01-19  1:04           ` Andrew Morton
2020-01-19 21:57             ` David Rientjes
2020-01-19 21:57               ` David Rientjes

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