From: NeilBrown <neilb@suse.de>
Date: Fri, 23 Jun 2006 09:05:48 +0000 (-0700)
Subject: [PATCH] Remove semi-softlockup from invalidate_mapping_pages
X-Git-Tag: Ubuntu-5.2.0-15.16~50718^2~38
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=e0f23603fb2607315ce52432cc4225df410828cf;p=mirror_ubuntu-eoan-kernel.git

[PATCH] Remove semi-softlockup from invalidate_mapping_pages

If invalidate_mapping_pages is called to invalidate a very large mapping
(e.g.  a very large block device) and if the only active page in that
device is near the end (or at least, at a very large index), such as, say,
the superblock of an md array, and if that page happens to be locked when
invalidate_mapping_pages is called, then

  pagevec_lookup will return this page and
  as it is locked, 'next' will be incremented and pagevec_lookup
  will be called again. and again. and again.
  while we count from 0 upto a very large number.

We should really always set 'next' to 'page->index+1' before going around
the loop again, not just if the page isn't locked.

Cc: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/mm/truncate.c b/mm/truncate.c
index 6cb3fff25f67..cf1b015df4a7 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -230,14 +230,24 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
 			pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
 		for (i = 0; i < pagevec_count(&pvec); i++) {
 			struct page *page = pvec.pages[i];
+			pgoff_t index;
+			int lock_failed;
 
-			if (TestSetPageLocked(page)) {
-				next++;
-				continue;
-			}
-			if (page->index > next)
-				next = page->index;
+			lock_failed = TestSetPageLocked(page);
+
+			/*
+			 * We really shouldn't be looking at the ->index of an
+			 * unlocked page.  But we're not allowed to lock these
+			 * pages.  So we rely upon nobody altering the ->index
+			 * of this (pinned-by-us) page.
+			 */
+			index = page->index;
+			if (index > next)
+				next = index;
 			next++;
+			if (lock_failed)
+				continue;
+
 			if (PageDirty(page) || PageWriteback(page))
 				goto unlock;
 			if (page_mapped(page))