Hello,
On Sat 22-08-20 16:22:16, Ye Bin wrote:
> Ye Bin (2):
> ext4: Add comment to BUFFER_FLAGS_DISCARD for search code
> jbd2: Fix race between do_invalidatepage and init_page_buffers
>
> fs/buffer.c | 12 +++++++++++-
> fs/jbd2/journal.c | 7 +++++++
> include/linux/buffer_head.h | 2 ++
> 3 files changed, 20 insertions(+), 1 deletion(-)
Thanks for the good description of the problem and the analysis. I could
now easily understand what was really happening on your system. I think the
problem should be fixed differently through - it is a problem of
block_write_full_page() that it invalidates buffers while JBD2 is working
with them. Attached patch should also fix the problem. Can you please test
whether it fixes your testcase as well? Thanks!
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
>From 3b568c008a995d3d24ea9e5ed4315a96deb0e598 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@xxxxxxx>
Date: Mon, 24 Aug 2020 17:07:40 +0200
Subject: [PATCH] fs: Don't invalidate page buffers in block_write_full_page()
If block_write_full_page() is called for a page that is beyond current
inode size, it will truncate page buffers for the page and return 0.
This logic has been added in 2.5.62 in commit 81eb69062588 ("fix ext3
BUG due to race with truncate") in history.git tree to fix a problem
with ext3 in data=ordered mode. This particular problem doesn't exist
anymore because ext3 is long gone and ext4 handles ordered data
differently. Also normally buffers are invalidated by truncate code and
there's no need to specially handle this in ->writepage() code.
This invalidation of page buffers in block_write_full_page() is causing
issues to filesystems (e.g. ext4 or ocfs2) when block device is shrunk
under filesystem's hands and metadata buffers get discarded while being
tracked by the journalling layer. Although it is obviously "not
supported" it can cause kernel crashes like:
[ 7986.689400] BUG: unable to handle kernel NULL pointer dereference at
+0000000000000008
[ 7986.697197] PGD 0 P4D 0
[ 7986.699724] Oops: 0002 [#1] SMP PTI
[ 7986.703200] CPU: 4 PID: 203778 Comm: jbd2/dm-3-8 Kdump: loaded Tainted: G
+O --------- - - 4.18.0-147.5.0.5.h126.eulerosv2r9.x86_64 #1
[ 7986.716438] Hardware name: Huawei RH2288H V3/BC11HGSA0, BIOS 1.57 08/11/2015
[ 7986.723462] RIP: 0010:jbd2_journal_grab_journal_head+0x1b/0x40 [jbd2]
...
[ 7986.810150] Call Trace:
[ 7986.812595] __jbd2_journal_insert_checkpoint+0x23/0x70 [jbd2]
[ 7986.818408] jbd2_journal_commit_transaction+0x155f/0x1b60 [jbd2]
[ 7986.836467] kjournald2+0xbd/0x270 [jbd2]
which is not great. The crash happens because bh->b_private is suddently
NULL although BH_JBD flag is still set (this is because
block_invalidatepage() cleared BH_Mapped flag and subsequent bh lookup
found buffer without BH_Mapped set, called init_page_buffers() which has
rewritten bh->b_private). So just remove the invalidation in
block_write_full_page().
Note that the buffer cache invalidation when block device changes size
is already careful to avoid similar problems by using
invalidate_mapping_pages() which skips busy buffers so it was only this
odd block_write_full_page() behavior that could tear down bdev buffers
under filesystem's hands.
Reported-by: Ye Bin <yebin10@xxxxxxxxxx>
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/buffer.c | 16 ----------------
1 file changed, 16 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 061dd202979d..163c2c0b9aa3 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2771,16 +2771,6 @@ int nobh_writepage(struct page *page, get_block_t *get_block,
/* Is the page fully outside i_size? (truncate in progress) */
offset = i_size & (PAGE_SIZE-1);
if (page->index >= end_index+1 || !offset) {
- /*
- * The page may have dirty, unmapped buffers. For example,
- * they may have been added in ext3_writepage(). Make them
- * freeable here, so the page does not leak.
- */
-#if 0
- /* Not really sure about this - do we need this ? */
- if (page->mapping->a_ops->invalidatepage)
- page->mapping->a_ops->invalidatepage(page, offset);
-#endif
unlock_page(page);
return 0; /* don't care */
}
@@ -2975,12 +2965,6 @@ int block_write_full_page(struct page *page, get_block_t *get_block,
/* Is the page fully outside i_size? (truncate in progress) */
offset = i_size & (PAGE_SIZE-1);
if (page->index >= end_index+1 || !offset) {
- /*
- * The page may have dirty, unmapped buffers. For example,
- * they may have been added in ext3_writepage(). Make them
- * freeable here, so the page does not leak.
- */
- do_invalidatepage(page, 0, PAGE_SIZE);
unlock_page(page);
return 0; /* don't care */
}
--
2.16.4
