From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 068/118] mm, thp: fix defrag setting if newline is not used Date: Thu, 30 Jan 2020 22:14:48 -0800 Message-ID: <20200131061448.X-yKx71ZM%akpm@linux-foundation.org> References: <20200130221021.5f0211c56346d5485af07923@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:34646 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725907AbgAaGOu (ORCPT ); Fri, 31 Jan 2020 01:14:50 -0500 In-Reply-To: <20200130221021.5f0211c56346d5485af07923@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, linux-mm@kvack.org, mgorman@techsingularity.net, mm-commits@vger.kernel.org, rientjes@google.com, torvalds@linux-foundation.org, vbabka@suse.cz From: David Rientjes Subject: mm, thp: fix defrag setting if newline is not used 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. Use the more appropriate sysfs_streq() that handles the trailing newline for us. Since this doubles as a nice cleanup, do it in enabled_store() as well. The current implementation relies on prefix matching: the number of bytes compared is either the number of bytes written or the length of the option being compared. With a newline, "defer\n" does not match "defer+"madvise"; without a newline, however, "defer" is considered to match "defer+madvise" (prefix matching is only comparing the first five bytes). End result is that writing "defer" is broken unless it has an additional trailing character. This means that writing "madv" in the past would match and set "madvise". With strict checking, that no longer is the case but it is unlikely anybody is currently doing this. Link: http://lkml.kernel.org/r/alpine.DEB.2.21.2001171411020.56385@chino.kir.corp.google.com Fixes: 21440d7eb904 ("mm, thp: add new defer+madvise defrag option") Signed-off-by: David Rientjes Suggested-by: Andrew Morton Acked-by: Vlastimil Babka Cc: Mel Gorman Signed-off-by: Andrew Morton --- mm/huge_memory.c | 24 ++++++++---------------- 1 file changed, 8 insertions(+), 16 deletions(-) --- a/mm/huge_memory.c~mm-thp-fix-defrag-setting-if-newline-is-not-used +++ a/mm/huge_memory.c @@ -177,16 +177,13 @@ static ssize_t enabled_store(struct kobj { ssize_t ret = count; - if (!memcmp("always", buf, - min(sizeof("always")-1, count))) { + if (sysfs_streq(buf, "always")) { clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags); set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags); - } else if (!memcmp("madvise", buf, - min(sizeof("madvise")-1, count))) { + } else if (sysfs_streq(buf, "madvise")) { clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags); set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags); - } else if (!memcmp("never", buf, - min(sizeof("never")-1, count))) { + } else if (sysfs_streq(buf, "never")) { clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags); clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags); } else @@ -250,32 +247,27 @@ static ssize_t defrag_store(struct kobje struct kobj_attribute *attr, const char *buf, size_t count) { - if (!memcmp("always", buf, - min(sizeof("always")-1, count))) { + if (sysfs_streq(buf, "always")) { 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 (sysfs_streq(buf, "defer+madvise")) { 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 (sysfs_streq(buf, "defer")) { 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 (sysfs_streq(buf, "madvise")) { 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 (sysfs_streq(buf, "never")) { 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); _