linux-kernel - [PATCH 3/3] mm: make PageReadahead more strict

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20200212221614.215302-3-minchan@kernel.org>
Date:   Wed, 12 Feb 2020 14:16:14 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>,
        Josef Bacik <josef@...icpanda.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Minchan Kim <minchan@...nel.org>, Robert Stupp <snazy@....de>
Subject: [PATCH 3/3] mm: make PageReadahead more strict

PG_readahead flag is shared with PG_reclaim but PG_reclaim is only
used in write context while PG_readahead is used for read context.

To make it clear, let's introduce PageReadahead wrapper with
!PageWriteback so it could make code clear and we could drop
PageWriteback check in page_cache_async_readahead, which removes
pointless dropping mmap_sem.

Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 include/linux/page-flags.h | 28 ++++++++++++++++++++++++++--
 mm/readahead.c             |  6 ------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 1bf83c8fcaa7..f91a9b2a49bd 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -363,8 +363,32 @@ PAGEFLAG(MappedToDisk, mappedtodisk, PF_NO_TAIL)
 /* PG_readahead is only used for reads; PG_reclaim is only for writes */
 PAGEFLAG(Reclaim, reclaim, PF_NO_TAIL)
 	TESTCLEARFLAG(Reclaim, reclaim, PF_NO_TAIL)
-PAGEFLAG(Readahead, reclaim, PF_NO_COMPOUND)
-	TESTCLEARFLAG(Readahead, reclaim, PF_NO_COMPOUND)
+
+SETPAGEFLAG(Readahead, reclaim, PF_NO_COMPOUND)
+CLEARPAGEFLAG(Readahead, reclaim, PF_NO_COMPOUND)
+
+/*
+ * Since PG_readahead is shared with PG_reclaim of the page flags,
+ * PageReadahead should double check whether it's readahead marker
+ * or PG_reclaim. It could be done by PageWriteback check because
+ * PG_reclaim is always with PG_writeback.
+ */
+static inline int PageReadahead(struct page *page)
+{
+	VM_BUG_ON_PGFLAGS(PageCompound(page), page);
+
+	return (page->flags & (1UL << PG_reclaim | 1UL << PG_writeback)) ==
+		(1UL << PG_reclaim);
+}
+
+/* Clear PG_readahead only if it's PG_readahead, not PG_reclaim */
+static inline int TestClearPageReadahead(struct page *page)
+{
+	VM_BUG_ON_PGFLAGS(PageCompound(page), page);
+
+	return !PageWriteback(page) ||
+			test_and_clear_bit(PG_reclaim, &page->flags);
+}
 
 #ifdef CONFIG_HIGHMEM
 /*
diff --git a/mm/readahead.c b/mm/readahead.c
index 2fe72cd29b47..85b15e5a1d7b 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -553,12 +553,6 @@ page_cache_async_readahead(struct address_space *mapping,
 	if (!ra->ra_pages)
 		return;
 
-	/*
-	 * Same bit is used for PG_readahead and PG_reclaim.
-	 */
-	if (PageWriteback(page))
-		return;
-
 	ClearPageReadahead(page);
 
 	/*
-- 
2.25.0.225.g125e21ebc7-goog