kernel.git/fs/btrfs/extent_map.c, branch linux-6.15.y

btrfs: do regular iput instead of delayed iput during extent map shrinking

2025-02-21T08:32:11Z

The extent map shrinker now runs in the system unbound workqueue and no longer in kswapd context so it can directly do an iput() on inodes even if that blocks or needs to acquire any lock (we aren't holding any locks when requesting the delayed iput from the shrinker). So we don't need to add a delayed iput, wake up the cleaner and delegate the iput() to the cleaner, which also adds extra contention on the spinlock that protects the delayed iputs list. Reported-by: Ivan Shapovalov Tested-by: Ivan Shapovalov Link: https://lore.kernel.org/linux-btrfs/0414d690ac5680d0d77dfc930606cdc36e42e12f.camel@intelfx.name/ CC: stable@vger.kernel.org # 6.12+ Reviewed-by: Johannes Thumshirn Reviewed-by: Qu Wenruo Signed-off-by: Filipe Manana Signed-off-by: David Sterba

btrfs: skip inodes without loaded extent maps when shrinking extent maps

2025-02-21T08:32:07Z

If there are inodes that don't have any loaded extent maps, we end up grabbing a reference on them and later adding a delayed iput, which wakes up the cleaner and makes it do unnecessary work. This is common when for example the inodes were open only to run stat(2) or all their extent maps were already released through the folio release callback (btrfs_release_folio()) or released by a previous run of the shrinker, or directories which never have extent maps. Reported-by: Ivan Shapovalov Tested-by: Ivan Shapovalov Link: https://lore.kernel.org/linux-btrfs/0414d690ac5680d0d77dfc930606cdc36e42e12f.camel@intelfx.name/ CC: stable@vger.kernel.org # 6.13+ Reviewed-by: Johannes Thumshirn Reviewed-by: Qu Wenruo Signed-off-by: Filipe Manana Signed-off-by: David Sterba

btrfs: fix use-after-free on inode when scanning root during em shrinking

2025-02-21T08:31:48Z

At btrfs_scan_root() we are accessing the inode's root (and fs_info) in a call to btrfs_fs_closing() after we have scheduled the inode for a delayed iput, and that can result in a use-after-free on the inode in case the cleaner kthread does the iput before we dereference the inode in the call to btrfs_fs_closing(). Fix this by using the fs_info stored already in a local variable instead of doing inode->root->fs_info. Fixes: 102044384056 ("btrfs: make the extent map shrinker run asynchronously as a work queue job") CC: stable@vger.kernel.org # 6.13+ Tested-by: Ivan Shapovalov Link: https://lore.kernel.org/linux-btrfs/0414d690ac5680d0d77dfc930606cdc36e42e12f.camel@intelfx.name/ Reviewed-by: Johannes Thumshirn Reviewed-by: Qu Wenruo Signed-off-by: Filipe Manana Signed-off-by: David Sterba

btrfs: rename extent map shrinker members from struct btrfs_fs_info

2024-11-11T13:34:17Z

The names for the members of struct btrfs_fs_info related to the extent map shrinker are a bit too long, so rename them to be shorter by replacing the "extent_map_" prefix with the "em_" prefix. Reviewed-by: Josef Bacik Signed-off-by: Filipe Manana Signed-off-by: David Sterba

btrfs: simplify tracking progress for the extent map shrinker

2024-11-11T13:34:17Z

Now that the extent map shrinker can only be run by a single task (as a work queue item) there is no need to keep the progress of the shrinker protected by a spinlock and passing the progress to trace events as parameters. So remove the lock and simplify the arguments for the trace events. Reviewed-by: Josef Bacik Signed-off-by: Filipe Manana Signed-off-by: David Sterba

btrfs: make the extent map shrinker run asynchronously as a work queue job

2024-11-11T13:34:17Z

Currently the extent map shrinker is run synchronously for kswapd tasks that end up calling the fs shrinker (fs/super.c:super_cache_scan()). This has some disadvantages and for some heavy workloads with memory pressure it can cause some delays and stalls that make a machine unresponsive for some periods. This happens because: 1) We can have several kswapd tasks on machines with multiple NUMA zones, and running the extent map shrinker concurrently can cause high contention on some spin locks, namely the spin locks that protect the radix tree that tracks roots, the per root xarray that tracks open inodes and the list of delayed iputs. This not only delays the shrinker but also causes high CPU consumption and makes the task running the shrinker monopolize a core, resulting in the symptoms of an unresponsive system. This was noted in previous commits such as commit ae1e766f623f ("btrfs: only run the extent map shrinker from kswapd tasks"); 2) The extent map shrinker's iteration over inodes can often be slow, even after changing the data structure that tracks open inodes for a root from a red black tree (up to kernel 6.10) to an xarray (kernel 6.10+). The transition to the xarray while it made things a bit faster, it's still somewhat slow - for example in a test scenario with 10000 inodes that have no extent maps loaded, the extent map shrinker took between 5ms to 8ms, using a release, non-debug kernel. Iterating over the extent maps of an inode can also be slow if have an inode with many thousands of extent maps, since we use a red black tree to track and search extent maps. So having the extent map shrinker run synchronously adds extra delay for other things a kswapd task does. So make the extent map shrinker run asynchronously as a job for the system unbounded workqueue, just like what we do for data and metadata space reclaim jobs. Reviewed-by: Josef Bacik Signed-off-by: Filipe Manana Signed-off-by: David Sterba

btrfs: add and use helper to remove extent map from its inode's tree

2024-11-11T13:34:17Z

Move the common code to remove an extent map from its inode's tree into a helper function and use it, reducing duplicated code. Reviewed-by: Josef Bacik Signed-off-by: Filipe Manana Signed-off-by: David Sterba

btrfs: correct typos in multiple comments across various files

2024-11-11T13:34:14Z

Fix some confusing spelling errors that were currently identified, the details are as follows: block-group.c: 2800: uncompressible ==> incompressible extent-tree.c: 3131: EXTEMT ==> EXTENT extent_io.c: 3124: utlizing ==> utilizing extent_map.c: 1323: ealier ==> earlier extent_map.c: 1325: possiblity ==> possibility fiemap.c: 189: emmitted ==> emitted fiemap.c: 197: emmitted ==> emitted fiemap.c: 203: emmitted ==> emitted transaction.h: 36: trasaction ==> transaction volumes.c: 5312: filesysmte ==> filesystem zoned.c: 1977: trasnsaction ==> transaction Signed-off-by: Shen Lichuan Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: fix extent map merging not happening for adjacent extents

2024-10-31T15:45:16Z

If we have 3 or more adjacent extents in a file, that is, consecutive file extent items pointing to adjacent extents, within a contiguous file range and compatible flags, we end up not merging all the extents into a single extent map. For example: $ mkfs.btrfs -f /dev/sdc $ mount /dev/sdc /mnt/sdc $ xfs_io -f -d -c "pwrite -b 64K 0 64K" \ -c "pwrite -b 64K 64K 64K" \ -c "pwrite -b 64K 128K 64K" \ -c "pwrite -b 64K 192K 64K" \ /mnt/sdc/foo After all the ordered extents complete we unpin the extent maps and try to merge them, but instead of getting a single extent map we get two because: 1) When the first ordered extent completes (file range [0, 64K)) we unpin its extent map and attempt to merge it with the extent map for the range [64K, 128K), but we can't because that extent map is still pinned; 2) When the second ordered extent completes (file range [64K, 128K)), we unpin its extent map and merge it with the previous extent map, for file range [0, 64K), but we can't merge with the next extent map, for the file range [128K, 192K), because this one is still pinned. The merged extent map for the file range [0, 128K) gets the flag EXTENT_MAP_MERGED set; 3) When the third ordered extent completes (file range [128K, 192K)), we unpin its extent map and attempt to merge it with the previous extent map, for file range [0, 128K), but we can't because that extent map has the flag EXTENT_MAP_MERGED set (mergeable_maps() returns false due to different flags) while the extent map for the range [128K, 192K) doesn't have that flag set. We also can't merge it with the next extent map, for file range [192K, 256K), because that one is still pinned. At this moment we have 3 extent maps: One for file range [0, 128K), with the flag EXTENT_MAP_MERGED set. One for file range [128K, 192K). One for file range [192K, 256K) which is still pinned; 4) When the fourth and final extent completes (file range [192K, 256K)), we unpin its extent map and attempt to merge it with the previous extent map, for file range [128K, 192K), which succeeds since none of these extent maps have the EXTENT_MAP_MERGED flag set. So we end up with 2 extent maps: One for file range [0, 128K), with the flag EXTENT_MAP_MERGED set. One for file range [128K, 256K), with the flag EXTENT_MAP_MERGED set. Since after merging extent maps we don't attempt to merge again, that is, merge the resulting extent map with the one that is now preceding it (and the one following it), we end up with those two extent maps, when we could have had a single extent map to represent the whole file. Fix this by making mergeable_maps() ignore the EXTENT_MAP_MERGED flag. While this doesn't present any functional issue, it prevents the merging of extent maps which allows to save memory, and can make defrag not merging extents too (that will be addressed in the next patch). Fixes: 199257a78bb0 ("btrfs: defrag: don't use merged extent map for their generation check") CC: stable@vger.kernel.org # 6.1+ Reviewed-by: Qu Wenruo Signed-off-by: Filipe Manana Signed-off-by: David Sterba

btrfs: fix read corruption due to race with extent map merging

2024-10-22T14:10:13Z

In debugging some corrupt squashfs files, we observed symptoms of corrupt page cache pages but correct on-disk contents. Further investigation revealed that the exact symptom was a correct page followed by an incorrect, duplicate, page. This got us thinking about extent maps. commit ac05ca913e9f ("Btrfs: fix race between using extent maps and merging them") enforces a reference count on the primary `em` extent_map being merged, as that one gets modified. However, since, commit 3d2ac9922465 ("btrfs: introduce new members for extent_map") both 'em' and 'merge' get modified, which started modifying 'merge' and thus introduced the same race. We were able to reproduce this by looping the affected squashfs workload in parallel on a bunch of separate btrfs-es while also dropping caches. We are still working on a simple enough reproducer to make into an fstest. The simplest fix is to stop modifying 'merge', which is not essential, as it is dropped immediately after the merge. This behavior is simply a consequence of the order of the two extent maps being important in computing the new values. Modify merge_ondisk_extents to take prev and next by const* and also take a third merged parameter that it puts the results in. Note that this introduces the rather odd behavior of passing 'em' to merge_ondisk_extents as a const * and as a regular ptr. Fixes: 3d2ac9922465 ("btrfs: introduce new members for extent_map") CC: stable@vger.kernel.org # 6.11+ Reviewed-by: Qu Wenruo Reviewed-by: Filipe Manana Signed-off-by: Omar Sandoval Signed-off-by: Boris Burkov Signed-off-by: David Sterba