kernel/linux.git/fs/dcache.c, branch v7.2-rc1

Merge tag 'pull-dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2026-06-14T22:45:31+00:00

Pull dcache updates from Al Viro: - d_alloc_parallel() API change (Neil's with my changes) - NORCU fixes - Reorganization and simplification of dentry eviction logic - Simplifying rcu_read_lock() scopes in fs/dcache.c - Secondary roots work - getting rid of NFS fake root dentries and dealing with remaining shrink_dcache_for_umount() and shrink_dentry_list() races - making cursors NORCU (surprisingly easy) * tag 'pull-dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (22 commits) make cursors NORCU nfs: get rid of fake root dentries wind ->s_roots via ->d_sib instead of ->d_hash shrink_dentry_tree(): unify the calls of shrink_dentry_list() shrinking rcu_read_lock() scope in d_alloc_parallel() d_walk(): shrink rcu_read_lock() scope document dentry_kill() adjust calling conventions of lock_for_kill(), fold __dentry_kill() into dentry_kill() Document rcu_read_lock() use in select_collect2() Shift rcu_read_{,un}lock() inside fast_dput() simplify safety for lock_for_kill() slowpath fold lock_for_kill() and __dentry_kill() into common helper fold lock_for_kill() into shrink_kill() shrink_dentry_list(): start with removing from shrink list d_prune_aliases(): make sure to skip NORCU aliases kill d_dispose_if_unused() make to_shrink_list() return whether it has moved dentry to list select_collect(): ignore dentries on shrink lists if they have positive refcounts find_acceptable_alias(): skip NORCU aliases with zero refcount fix a race between d_find_any_alias() and final dput() of NORCU dentries ...

Merge tag 'vfs-7.2-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2026-06-14T22:29:45+00:00

Pull misc vfs updates from Christian Brauner: "Features: - Reduce pipe->mutex contention by pre-allocating pages outside the lock in anon_pipe_write(). anon_pipe_write() called alloc_page() once per page while holding pipe->mutex. The allocation can sleep doing direct reclaim and runs memcg charging, which extends the critical section and stalls any concurrent reader on the same mutex. Now up to 8 pages are pre-allocated before the mutex is taken, leftovers are recycled into the per-pipe tmp_page[] cache before unlock, and any remainder is released after unlock, keeping the allocator out of the critical section on both sides. On a writers x readers sweep with 64KB writes against a 1 MB pipe throughput improves 6-28% and average write latency drops 5-22%; under memory pressure - when the cost of holding the mutex across reclaim is highest - throughput improves 21-48% and latency drops 17-33%. The microbenchmark is added to selftests. - uaccess/sockptr: fix the ignored_trailing logic in copy_struct_to_user() to behave as documented and the usize check in copy_struct_from_sockptr() for user pointers, and add copy_struct_{from,to}_bounce_buffer() and copy_struct_to_sockptr() helpers for upcoming users (IPPROTO_SMBDIRECT, IPPROTO_QUIC). - bpf: add a sleepable bpf_real_inode() kfunc that resolves the real inode backing a dentry via d_real_inode(). On overlayfs the inode attached to the dentry doesn't carry the underlying device information; this is used by the filesystem restriction BPF program that was merged into systemd. - docs: add guidelines for submitting new filesystems, motivated by the maintenance burden abandoned and untestable filesystems impose on VFS developers, blocking infrastructure work like folio conversions and iomap migration. Fixes: - libfs: set SB_I_NOEXEC and SB_I_NODEV by default in init_pseudo() and drop the now-redundant assignments in callers. This began as a one-line dma-buf fix for a path_noexec() warning; a pseudo filesystem has no reason not to set SB_I_NOEXEC. All init_pseudo() callers were audited: the only visible effect is on dma-buf where SB_I_NOEXEC silences the warning. - Handle set_blocksize() failures in legacy filesystems (bfs, hpfs, qnx4, jfs, befs, affs, isofs, minix, ntfs3, omfs). Mounting a device with a sector size > PAGE_SIZE crashed roughly half of them; the rest had the same missing error handling pattern. Plus a follow-up releasing the superblock buffer_head when setting the minix v3 block size fails. - mount: honour SB_NOUSER in the new mount API. - fs/fcntl: fix a SOFTIRQ-unsafe lock order in fasync signaling by switching the process-group paths of send_sigio() and send_sigurg() from read_lock(&tasklist_lock) to RCU, matching the single-PID path. - vfs: add an FS_USERNS_DELEGATABLE flag and set it for NFS, fixing delegated NFS mounts (fsopen() in a container with the mount performed by a privileged daemon) that broke when non-init s_user_ns was tied to FS_USERNS_MOUNT. - selftests/namespaces: fix a hang in nsid_test where an unreaped grandchild kept the TAP pipe write-end open, a waitpid(-1) race in listns_efault_test, and a false FAIL on kernels without listns() where the tests should SKIP. - filelock: fix the break_lease() stub signature for CONFIG_FILE_LOCKING=n. - init/initramfs_test: wait for the async initramfs unpacking before running; the test and do_populate_rootfs() share the parser state. - fs/coredump: reduce redundant log noise in validate_coredump_safety(). - iomap: pass the correct length to fserror_report_io() in __iomap_write_begin(). - backing-file: fix the backing_file_open() kerneldoc. Cleanups: - initramfs: refactor the cpio hex header parsing to use hex2bin() instead of the hand-rolled simple_strntoul() which is reverted, and extend the initramfs KUnit tests to cover header fields with 0x prefixes. - Replace __get_free_pages() and friends with kmalloc()/kzalloc() across quota, proc, ocfs2/dlm, nilfs2, nfs, nfsd, libfs, jfs, jbd2, isofs, fuse, select, namespace, configfs, binfmt_misc, bfs, and the do_mounts init code - part of the larger work of replacing page allocator calls with kmalloc(). - Use clear_and_wake_up_bit() in unlock_buffer() and journal_end_buffer_io_sync() instead of open-coding the sequence. - Drop unused VFS exports: unexport drop_super_exclusive(), remove start_removing_user_path_at(), and fold __start_removing_path() into start_removing_path(). - fs/read_write: narrow the __kernel_write() export with EXPORT_SYMBOL_FOR_MODULES(). - vfs: uapi: retire octal and hex constants in favor of (1 << n) for the O_ flags. Finding a free bit for a new flag across the architectures was needlessly hard with the mixed bases. - dcache: add extra sanity checks of dead dentries in dentry_free() via a new DENTRY_WARN_ONCE() that also prints d_flags. - iov_iter: use kmemdup_array() in dup_iter() to harden the allocation against multiplication overflow. - fs/pipe: write to ->poll_usage only once. - vfs: remove an always-taken if-branch in find_next_fd(). - dcache: use kmalloc_flex() for struct external_name in __d_alloc(). - namei: use QSTR() instead of QSTR_INIT() in path_pts(). - sync_file_range: delete dead S_ISLNK code. - Comment fixes: retire a stale comment in fget_task_next() and fix assorted spelling mistakes" * tag 'vfs-7.2-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (73 commits) backing-file: fix backing_file_open() kerneldoc parameter iomap: pass the correct len to fserror_report_io in __iomap_write_begin vfs: add FS_USERNS_DELEGATABLE flag and set it for NFS filelock: fix break_lease() stub signature for CONFIG_FILE_LOCKING=n vfs: uapi: retire octal and hex numbers in favor of (1 << n) for O_ flags bpf: add bpf_real_inode() kfunc fs/read_write: Do not export __kernel_write() to the entire world libfs: drop redundant SB_I_NOEXEC/SB_I_NODEV in init_pseudo() callers libfs: set SB_I_NOEXEC and SB_I_NODEV by default in init_pseudo() mount: honour SB_NOUSER in the new mount API fs/fcntl: fix SOFTIRQ-unsafe lock order in fasync signaling selftests/pipe: add pipe_bench microbenchmark fs/pipe: pre-allocate pages outside pipe->mutex in anon_pipe_write fs: retire stale comment in fget_task_next() fs: fix spelling mistakes in comment bfs: replace get_zeroed_page() with kzalloc() binfmt_misc: replace __get_free_page() with kmalloc() configfs: replace __get_free_pages() with kzalloc() fs/namespace: use __getname() to allocate mntpath buffer fs/select: replace __get_free_page() with kmalloc() ...

make cursors NORCU

2026-06-05T04:34:56+00:00

All it requires is making sure that d_walk() will skip *all* CURSOR dentries, even if somebody passes it one as an argument. Cursors are negative and unhashed all along, never get added to LRU or to shrink lists and no RCU references via ->d_sib are possible for those - dentry_unlist() makes sure that no killed dentry has ->d_sib.next left pointing to a cursor. Seeing that a cursor is allocated every time we open a directory on autofs, debugfs, devpts, etc., avoiding an RCU delay when such opened files get closed is attractive... Signed-off-by: Al Viro

nfs: get rid of fake root dentries

2026-06-05T04:34:56+00:00

... just grab the reference to the (real) root we are about to return for the first mount of this superblock and be done with that. Once upon a time dentry tree eviction at fs shutdown used to break if ->s_root had been spliced on top of something; that hadn't been the case for years now, and these fake root dentries violate a bunch of invariants. Let's get rid of them... Signed-off-by: Al Viro

wind ->s_roots via ->d_sib instead of ->d_hash

2026-06-05T04:34:56+00:00

shrink_dcache_for_umount() is supposed to handle the possibility of some of the dentries to be evicted being in other threads shrink lists; it either kills them, leaving an empty husk to be freed by the owner of shrink list whenever it gets around to that, or it waits for the eviction in progress to get completed. That relies upon dentry remaining attached to the tree until the eviction reaches dentry_unlist() and its ->d_sib gets removed from the list. Unfortunately, the secondary roots are linked via ->d_hash, rather than ->d_sib and they become removed from that list before their inode references are dropped. If shrink_dentry_list() from another thread ends up evicting one of the secondary roots and gets to that point in dentry_kill() when shrink_dcache_for_umount() is looking for secondary roots, the latter will *not* notice anything, possibly leading to warnings about busy inodes at umount time and all kinds of breakage after that. Moreover, shrink_dcache_for_umount() walks the list of secondary roots with no protection whatsoever, so it might end up calling dget() on a dentry that already passed through lockref_mark_dead(&dentry->d_lockref); ending up with corrupted refcount and possible UAF. AFAICS, the most straightforward way to deal with that would be to have secondary roots linked via ->d_sib rather than ->d_hash; then they would remain on the list until killed, and we could use d_add_waiter() machinery to wait for eviction in progress. Changes: * secondary roots look the same as ->s_root from d_unhashed() and d_unlinked() POV now. * secondary roots are represented as "no parent, but on ->d_sib" instead of "no parent, but on ->d_hash". * since ->d_sib is a plain hlist, we protect it with per-superblock spinlock (sb->s_roots_lock) instead of the LSB of the head pointer (for non-root dentries it would be protected by ->d_lock of parent). * __d_obtain_alias() uses ->d_sib for linkage when allocating a secondary root. * d_splice_alias_ops() detects splicing of a secondary root and removes it from the list before calling __d_move(). * dentry_unlist() detects eviction of a secondary root and removes it from the list; no need to play the games for d_walk() sake, since the latter is not going to look for the next sibling of those anyway. * ___d_drop() doesn't care about ->s_roots anymore. * shrink_dcache_for_umount() uses proper locking for access to the list of secondary roots and if it runs into one that is in the middle of eviction waits for that to finish. Signed-off-by: Al Viro

shrink_dentry_tree(): unify the calls of shrink_dentry_list()

2026-06-05T04:34:55+00:00

Signed-off-by: Al Viro

shrinking rcu_read_lock() scope in d_alloc_parallel()

2026-06-05T04:34:55+00:00

The current use of rcu_read_lock() uses in d_alloc_parallel() is fairly opaque - the single large scope serves two purposes. We start with lookup in normal hash, and there rcu_read_lock() scope puts __d_lookup_rcu() and subsequent lockref_get_not_dead() into the same RCU read-side critical area. If no match is found, we proceed to lock the hash chain of in-lookup hash and scan that for a match. If we find a match, we want to grab it and wait for lookup in progress to finish. Since the bitlock we use for these hash chains has to nest inside ->d_lock, we need to unlock the chain first and use lockref_get_not_dead() on the match. That has to be done without breaking the RCU read-side critical area, and we use the same rcu_read_lock() scope to bridge over. The thing is, after having grabbed the reference (and it is very unlikely to fail) we proceed to grab ->d_lock - d_wait_lookup() and __d_lookup_unhash()/__d_wake_in_lookup_waiters() are using that for serialization. That makes lockref_get_not_dead() pointless - trying to avoid grabbing ->d_lock for refcount increment, only to grab it anyway immediately after that. If we grab ->d_lock first and replace lockref_get_not_dead() with direct check for sign and increment if non-negative we can move rcu_read_unlock() to immediately after grabbing ->d_lock. Moreover, we don't need the RCU read-side critical area to be contiguous since before earlier __d_lookup_rcu() - we can just as well terminate the earlier one ASAP and call rcu_read_lock() again only after having found a match (if any) in the in-lookup hash chain. That makes the entire thing easier to follow and the purpose of those rcu_read_lock() calls easier to describe - the first scope is for __d_lookup_rcu() + lockref_get_not_dead(), the second one bridges over from the bitlock scope to the ->d_lock scope on the match found in in-lookup hash. Signed-off-by: Al Viro

d_walk(): shrink rcu_read_lock() scope

2026-06-05T04:34:55+00:00

we only need it to bridge over from ->d_lock scope of child to ->d_lock scope of parent; dropping ->d_lock at rename_retry doesn't need to be in rcu_read_lock() scope. Signed-off-by: Al Viro

document dentry_kill()

2026-06-05T04:34:55+00:00

Signed-off-by: Al Viro

adjust calling conventions of lock_for_kill(), fold __dentry_kill() into dentry_kill()

2026-06-05T04:34:55+00:00

Pull dropping ->d_lock on lock_for_kill() failure into lock_for_kill() itself. That reduces dentry_kill() to if (!lock_for_kill(dentry)) return NULL; return __dentry_kill(dentry); at which point it's easier to move that if (...) into the beginning of __dentry_kill() itself and rename it into dentry_kill(). Document the new calling conventions of lock_for_kill(). Signed-off-by: Al Viro