LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>, stable@vger.kernel.org
Subject: [PATCH] mm: Remove bogus VM_BUG_ON
Date: Wed, 18 Aug 2021 15:49:32 +0100	[thread overview]
Message-ID: <20210818144932.940640-1-willy@infradead.org> (raw)

It is not safe to check page->index without holding the page lock.
It can be changed if the page is moved between the swap cache and the
page cache for a shmem file, for example.  There is a VM_BUG_ON below
which checks page->index is correct after taking the page lock.

Cc: stable@vger.kernel.org
Fixes: 5c211ba29deb ("mm: add and use find_lock_entries")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/filemap.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index d1458ecf2f51..34de0b14aaa9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2033,17 +2033,16 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
 	XA_STATE(xas, &mapping->i_pages, start);
 	struct page *page;
 
 	rcu_read_lock();
 	while ((page = find_get_entry(&xas, end, XA_PRESENT))) {
 		if (!xa_is_value(page)) {
 			if (page->index < start)
 				goto put;
-			VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
 			if (page->index + thp_nr_pages(page) - 1 > end)
 				goto put;
 			if (!trylock_page(page))
 				goto put;
 			if (page->mapping != mapping || PageWriteback(page))
 				goto unlock;
 			VM_BUG_ON_PAGE(!thp_contains(page, xas.xa_index),
 					page);
-- 
2.30.2


             reply	other threads:[~2021-08-18 14:51 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-18 14:49 Matthew Wilcox (Oracle) [this message]
2021-08-18 16:34 ` Hugh Dickins
2021-08-18 16:45   ` Matthew Wilcox
2021-08-19 20:42     ` Hugh Dickins

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210818144932.940640-1-willy@infradead.org \
    --to=willy@infradead.org \
    --cc=akpm@linux-foundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=stable@vger.kernel.org \
    --subject='Re: [PATCH] mm: Remove bogus VM_BUG_ON' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).