From: Hugh Dickins <hughd@google.com>
Date: Fri, 30 Nov 2018 22:10:25 +0000 (-0800)
Subject: mm/khugepaged: collapse_shmem() stop if punched or truncated
X-Git-Tag: android-x86-7.1-r3~7^2~75^2~46
X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=10e458e6eb59e533e499269258b6069392bec627;p=android-x86%2Fkernel.git

mm/khugepaged: collapse_shmem() stop if punched or truncated

commit 701270fa193aadf00bdcf607738f64997275d4c7 upstream.

Huge tmpfs testing showed that although collapse_shmem() recognizes a
concurrently truncated or hole-punched page correctly, its handling of
holes was liable to refill an emptied extent.  Add check to stop that.

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261522040.2275@eggly.anvils
Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: <stable@vger.kernel.org>	[4.8+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 1df37ee996d5..62de24194f24 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1352,6 +1352,16 @@ static void collapse_shmem(struct mm_struct *mm,
 		int n = min(iter.index, end) - index;
 
 		/*
+		 * Stop if extent has been hole-punched, and is now completely
+		 * empty (the more obvious i_size_read() check would take an
+		 * irq-unsafe seqlock on 32-bit).
+		 */
+		if (n >= HPAGE_PMD_NR) {
+			result = SCAN_TRUNCATED;
+			goto tree_locked;
+		}
+
+		/*
 		 * Handle holes in the radix tree: charge it from shmem and
 		 * insert relevant subpage of new_page into the radix-tree.
 		 */
@@ -1462,6 +1472,11 @@ out_unlock:
 	if (result == SCAN_SUCCEED && index < end) {
 		int n = end - index;
 
+		/* Stop if extent has been truncated, and is now empty */
+		if (n >= HPAGE_PMD_NR) {
+			result = SCAN_TRUNCATED;
+			goto tree_locked;
+		}
 		if (!shmem_charge(mapping->host, n)) {
 			result = SCAN_FAIL;
 			goto tree_locked;