The cached writeback mapping is EOF trimmed to try and avoid races between post-eof block management and writeback that result in sending cached data to a stale location. The cached mapping is currently trimmed on the validation check, which leaves a race window between the time the mapping is cached and when it is trimmed against the current inode size.
For example, if a new mapping is cached by delalloc conversion on a blocksize == page size fs, we could cycle various locks, perform memory allocations, etc. in the writeback codepath before the associated mapping is eventually trimmed to i_size. This leaves enough time for a post-eof truncate and file append before the cached mapping is trimmed. The former event essentially invalidates a range of the cached mapping and the latter bumps the inode size such the trim on the next writepage event won't trim all of the invalid blocks. fstest generic/464 reproduces this scenario occasionally and causes a lost writeback and stale delalloc blocks warning on inode inactivation.
To work around this problem, trim the cached writeback mapping as soon as it is cached in addition to on subsequent validation checks. This is a minor tweak to tighten the race window as much as possible until a proper invalidation mechanism is available.
Fixes: 40214d128e07 ("xfs: trim writepage mapping to within eof") Cc: stable@vger.kernel.org # v4.14+ Signed-off-by: Brian Foster bfoster@redhat.com --- fs/xfs/xfs_aops.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c index 338b9d9984e0..d9048bcea49c 100644 --- a/fs/xfs/xfs_aops.c +++ b/fs/xfs/xfs_aops.c @@ -449,6 +449,7 @@ xfs_map_blocks( }
wpc->imap = imap; + xfs_trim_extent_eof(&wpc->imap, ip); trace_xfs_map_blocks_found(ip, offset, count, wpc->io_type, &imap); return 0; allocate_blocks: @@ -459,6 +460,7 @@ xfs_map_blocks( ASSERT(whichfork == XFS_COW_FORK || cow_fsb == NULLFILEOFF || imap.br_startoff + imap.br_blockcount <= cow_fsb); wpc->imap = imap; + xfs_trim_extent_eof(&wpc->imap, ip); trace_xfs_map_blocks_alloc(ip, offset, count, wpc->io_type, &imap); return 0; }
Hi,
[This is an automated email]
This commit has been processed because it contains a "Fixes:" tag, fixing commit: 40214d128e07 xfs: trim writepage mapping to within eof.
The bot has tested the following trees: v4.20.2, v4.19.15, v4.14.93, v4.9.150.
v4.20.2: Build OK! v4.19.15: Build OK! v4.14.93: Failed to apply! Possible dependencies: 2d5f4b5bebcc ("xfs: remove unused parameter from xfs_writepage_map") 5c665e5b5af6 ("xfs: remove xfs_map_cow") 70c57dcd606f ("xfs: skip CoW writes past EOF when writeback races with truncate") a7b28f72ab90 ("xfs: don't use XFS_BMAPI_IGSTATE in xfs_map_blocks") b4d8ad7fd3a1 ("xfs: fix s_maxbytes overflow problems")
v4.9.150: Failed to apply! Possible dependencies: 08438b1e386b ("xfs: plumb in needed functions for range querying of the freespace btrees") 092d5d9d5812 ("xfs: cleanup xfs_reflink_find_cow_mapping") 11ef38afe98c ("xfs: make xfs btree stats less huge") 2d5f4b5bebcc ("xfs: remove unused parameter from xfs_writepage_map") 5c665e5b5af6 ("xfs: remove xfs_map_cow") 70c57dcd606f ("xfs: skip CoW writes past EOF when writeback races with truncate") 755c7bf5ddca ("libxfs: convert ushort to unsigned short") a7b28f72ab90 ("xfs: don't use XFS_BMAPI_IGSTATE in xfs_map_blocks") af7d20fd83d9 ("xfs: make xfs_btree_magic more generic") b4d8ad7fd3a1 ("xfs: fix s_maxbytes overflow problems") c8ce540db5f6 ("xfs: remove double-underscore integer types") cae028df5344 ("xfs: optimise CRC updates")
How should we proceed with this patch?
-- Thanks, Sasha
On Wed, Jan 16, 2019 at 01:35:38PM +0000, Sasha Levin wrote:
Hi,
[This is an automated email]
This commit has been processed because it contains a "Fixes:" tag, fixing commit: 40214d128e07 xfs: trim writepage mapping to within eof.
The bot has tested the following trees: v4.20.2, v4.19.15, v4.14.93, v4.9.150.
v4.20.2: Build OK! v4.19.15: Build OK! v4.14.93: Failed to apply! Possible dependencies: 2d5f4b5bebcc ("xfs: remove unused parameter from xfs_writepage_map") 5c665e5b5af6 ("xfs: remove xfs_map_cow") 70c57dcd606f ("xfs: skip CoW writes past EOF when writeback races with truncate") a7b28f72ab90 ("xfs: don't use XFS_BMAPI_IGSTATE in xfs_map_blocks") b4d8ad7fd3a1 ("xfs: fix s_maxbytes overflow problems")
v4.9.150: Failed to apply! Possible dependencies: 08438b1e386b ("xfs: plumb in needed functions for range querying of the freespace btrees") 092d5d9d5812 ("xfs: cleanup xfs_reflink_find_cow_mapping") 11ef38afe98c ("xfs: make xfs btree stats less huge") 2d5f4b5bebcc ("xfs: remove unused parameter from xfs_writepage_map") 5c665e5b5af6 ("xfs: remove xfs_map_cow") 70c57dcd606f ("xfs: skip CoW writes past EOF when writeback races with truncate") 755c7bf5ddca ("libxfs: convert ushort to unsigned short") a7b28f72ab90 ("xfs: don't use XFS_BMAPI_IGSTATE in xfs_map_blocks") af7d20fd83d9 ("xfs: make xfs_btree_magic more generic") b4d8ad7fd3a1 ("xfs: fix s_maxbytes overflow problems") c8ce540db5f6 ("xfs: remove double-underscore integer types") cae028df5344 ("xfs: optimise CRC updates")
How should we proceed with this patch?
The writeback code in XFS has seen a decent amount of rework since these older kernels. I'm not quite sure how stable deals with these conflicts, but for reference, I think the appended (untested) diff is essentially equivalent for the above two kernels. It doesn't cover the xfs_map_cow() case in 4.14, but that code is experimental. Also note that the upstream patch is still technically not reviewed.
Brian
--- 8< ---
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c index b0cccf8a81a8..b93b3064de20 100644 --- a/fs/xfs/xfs_aops.c +++ b/fs/xfs/xfs_aops.c @@ -421,8 +421,10 @@ xfs_map_blocks( (!nimaps || isnullstartblock(imap->br_startblock))) { error = xfs_iomap_write_allocate(ip, XFS_DATA_FORK, offset, imap); - if (!error) + if (!error) { trace_xfs_map_blocks_alloc(ip, offset, count, type, imap); + xfs_trim_extent_eof(imap, ip); + } return error; }
@@ -433,8 +435,10 @@ xfs_map_blocks( ASSERT(imap->br_startblock != DELAYSTARTBLOCK); } #endif - if (nimaps) + if (nimaps) { trace_xfs_map_blocks_found(ip, offset, count, type, imap); + xfs_trim_extent_eof(imap, ip); + } return 0; }
linux-stable-mirror@lists.linaro.org
-
Brian Foster -
Sasha Levin