linux-rng/init, branch master

Merge tag 'core-rseq-2025-11-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2025-12-02T16:48:53Z

Pull rseq updates from Thomas Gleixner: "A large overhaul of the restartable sequences and CID management: The recent enablement of RSEQ in glibc resulted in regressions which are caused by the related overhead. It turned out that the decision to invoke the exit to user work was not really a decision. More or less each context switch caused that. There is a long list of small issues which sums up nicely and results in a 3-4% regression in I/O benchmarks. The other detail which caused issues due to extra work in context switch and task migration is the CID (memory context ID) management. It also requires to use a task work to consolidate the CID space, which is executed in the context of an arbitrary task and results in sporadic uncontrolled exit latencies. The rewrite addresses this by: - Removing deprecated and long unsupported functionality - Moving the related data into dedicated data structures which are optimized for fast path processing. - Caching values so actual decisions can be made - Replacing the current implementation with a optimized inlined variant. - Separating fast and slow path for architectures which use the generic entry code, so that only fault and error handling goes into the TIF_NOTIFY_RESUME handler. - Rewriting the CID management so that it becomes mostly invisible in the context switch path. That moves the work of switching modes into the fork/exit path, which is a reasonable tradeoff. That work is only required when a process creates more threads than the cpuset it is allowed to run on or when enough threads exit after that. An artificial thread pool benchmarks which triggers this did not degrade, it actually improved significantly. The main effect in migration heavy scenarios is that runqueue lock held time and therefore contention goes down significantly" * tag 'core-rseq-2025-11-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (54 commits) sched/mmcid: Switch over to the new mechanism sched/mmcid: Implement deferred mode change irqwork: Move data struct to a types header sched/mmcid: Provide CID ownership mode fixup functions sched/mmcid: Provide new scheduler CID mechanism sched/mmcid: Introduce per task/CPU ownership infrastructure sched/mmcid: Serialize sched_mm_cid_fork()/exit() with a mutex sched/mmcid: Provide precomputed maximal value sched/mmcid: Move initialization out of line signal: Move MMCID exit out of sighand lock sched/mmcid: Convert mm CID mask to a bitmap cpumask: Cache num_possible_cpus() sched/mmcid: Use cpumask_weighted_or() cpumask: Introduce cpumask_weighted_or() sched/mmcid: Prevent pointless work in mm_update_cpus_allowed() sched/mmcid: Move scheduler code out of global header sched: Fixup whitespace damage sched/mmcid: Cacheline align MM CID storage sched/mmcid: Use proper data structures sched/mmcid: Revert the complex CID management ...

Merge tag 'kernel-6.19-rc1.cred' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2025-12-01T21:45:41Z

Pull cred guard updates from Christian Brauner: "This contains substantial credential infrastructure improvements adding guard-based credential management that simplifies code and eliminates manual reference counting in many subsystems. Features: - Kernel Credential Guards Add with_kernel_creds() and scoped_with_kernel_creds() guards that allow using the kernel credentials without allocating and copying them. This was requested by Linus after seeing repeated prepare_kernel_creds() calls that duplicate the kernel credentials only to drop them again later. The new guards completely avoid the allocation and never expose the temporary variable to hold the kernel credentials anywhere in callers. - Generic Credential Guards Add scoped_with_creds() guards for the common override_creds() and revert_creds() pattern. This builds on earlier work that made override_creds()/revert_creds() completely reference count free. - Prepare Credential Guards Add prepare credential guards for the more complex pattern of preparing a new set of credentials and overriding the current credentials with them: - prepare_creds() - modify new creds - override_creds() - revert_creds() - put_cred() Cleanups: - Make init_cred static since it should not be directly accessed - Add kernel_cred() helper to properly access the kernel credentials - Fix scoped_class() macro that was introduced two cycles ago - coredump: split out do_coredump() from vfs_coredump() for cleaner credential handling - coredump: move revert_cred() before coredump_cleanup() - coredump: mark struct mm_struct as const - coredump: pass struct linux_binfmt as const - sev-dev: use guard for path" * tag 'kernel-6.19-rc1.cred' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (36 commits) trace: use override credential guard trace: use prepare credential guard coredump: use override credential guard coredump: use prepare credential guard coredump: split out do_coredump() from vfs_coredump() coredump: mark struct mm_struct as const coredump: pass struct linux_binfmt as const coredump: move revert_cred() before coredump_cleanup() sev-dev: use override credential guards sev-dev: use prepare credential guard sev-dev: use guard for path cred: add prepare credential guard net/dns_resolver: use credential guards in dns_query() cgroup: use credential guards in cgroup_attach_permissions() act: use credential guards in acct_write_process() smb: use credential guards in cifs_get_spnego_key() nfs: use credential guards in nfs_idmap_get_key() nfs: use credential guards in nfs_local_call_write() nfs: use credential guards in nfs_local_call_read() erofs: use credential guards ...

Merge tag 'namespace-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2025-12-01T17:47:41Z

Pull namespace updates from Christian Brauner: "This contains substantial namespace infrastructure changes including a new system call, active reference counting, and extensive header cleanups. The branch depends on the shared kbuild branch for -fms-extensions support. Features: - listns() system call Add a new listns() system call that allows userspace to iterate through namespaces in the system. This provides a programmatic interface to discover and inspect namespaces, addressing longstanding limitations: Currently, there is no direct way for userspace to enumerate namespaces. Applications must resort to scanning /proc/*/ns/ across all processes, which is: - Inefficient - requires iterating over all processes - Incomplete - misses namespaces not attached to any running process but kept alive by file descriptors, bind mounts, or parent references - Permission-heavy - requires access to /proc for many processes - No ordering or ownership information - No filtering per namespace type The listns() system call solves these problems: ssize_t listns(const struct ns_id_req *req, u64 *ns_ids, size_t nr_ns_ids, unsigned int flags); struct ns_id_req { __u32 size; __u32 spare; __u64 ns_id; struct /* listns */ { __u32 ns_type; __u32 spare2; __u64 user_ns_id; }; }; Features include: - Pagination support for large namespace sets - Filtering by namespace type (MNT_NS, NET_NS, USER_NS, etc.) - Filtering by owning user namespace - Permission checks respecting namespace isolation - Active Reference Counting Introduce an active reference count that tracks namespace visibility to userspace. A namespace is visible in the following cases: - The namespace is in use by a task - The namespace is persisted through a VFS object (namespace file descriptor or bind-mount) - The namespace is a hierarchical type and is the parent of child namespaces The active reference count does not regulate lifetime (that's still done by the normal reference count) - it only regulates visibility to namespace file handles and listns(). This prevents resurrection of namespaces that are pinned only for internal kernel reasons (e.g., user namespaces held by file->f_cred, lazy TLB references on idle CPUs, etc.) which should not be accessible via (1)-(3). - Unified Namespace Tree Introduce a unified tree structure for all namespaces with: - Fixed IDs assigned to initial namespaces - Lookup based solely on inode number - Maintained list of owned namespaces per user namespace - Simplified rbtree comparison helpers Cleanups - Header Reorganization: - Move namespace types into separate header (ns_common_types.h) - Decouple nstree from ns_common header - Move nstree types into separate header - Switch to new ns_tree_{node,root} structures with helper functions - Use guards for ns_tree_lock - Initial Namespace Reference Count Optimization - Make all reference counts on initial namespaces a nop to avoid pointless cacheline ping-pong for namespaces that can never go away - Drop custom reference count initialization for initial namespaces - Add NS_COMMON_INIT() macro and use it for all namespaces - pid: rely on common reference count behavior - Miscellaneous Cleanups - Rename exit_task_namespaces() to exit_nsproxy_namespaces() - Rename is_initial_namespace() and make argument const - Use boolean to indicate anonymous mount namespace - Simplify owner list iteration in nstree - nsfs: raise SB_I_NODEV, SB_I_NOEXEC, and DCACHE_DONTCACHE explicitly - nsfs: use inode_just_drop() - pidfs: raise DCACHE_DONTCACHE explicitly - pidfs: simplify PIDFD_GET__NAMESPACE ioctls - libfs: allow to specify s_d_flags - cgroup: add cgroup namespace to tree after owner is set - nsproxy: fix free_nsproxy() and simplify create_new_namespaces() Fixes: - setns(pidfd, ...) race condition Fix a subtle race when using pidfds with setns(). When the target task exits after prepare_nsset() but before commit_nsset(), the namespace's active reference count might have been dropped. If setns() then installs the namespaces, it would bump the active reference count from zero without taking the required reference on the owner namespace, leading to underflow when later decremented. The fix resurrects the ownership chain if necessary - if the caller succeeded in grabbing passive references, the setns() should succeed even if the target task exits or gets reaped. - Return EFAULT on put_user() error instead of success - Make sure references are dropped outside of RCU lock (some namespaces like mount namespace sleep when putting the last reference) - Don't skip active reference count initialization for network namespace - Add asserts for active refcount underflow - Add asserts for initial namespace reference counts (both passive and active) - ipc: enable is_ns_init_id() assertions - Fix kernel-doc comments for internal nstree functions - Selftests - 15 active reference count tests - 9 listns() functionality tests - 7 listns() permission tests - 12 inactive namespace resurrection tests - 3 threaded active reference count tests - commit_creds() active reference tests - Pagination and stress tests - EFAULT handling test - nsid tests fixes" * tag 'namespace-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (103 commits) pidfs: simplify PIDFD_GET__NAMESPACE ioctls nstree: fix kernel-doc comments for internal functions nsproxy: fix free_nsproxy() and simplify create_new_namespaces() selftests/namespaces: fix nsid tests ns: drop custom reference count initialization for initial namespaces pid: rely on common reference count behavior ns: add asserts for initial namespace active reference counts ns: add asserts for initial namespace reference counts ns: make all reference counts on initial namespace a nop ipc: enable is_ns_init_id() assertions fs: use boolean to indicate anonymous mount namespace ns: rename is_initial_namespace() ns: make is_initial_namespace() argument const nstree: use guards for ns_tree_lock nstree: simplify owner list iteration nstree: switch to new structures nstree: add helper to operate on struct ns_tree_{node,root} nstree: move nstree types into separate header nstree: decouple from ns_common header ns: move namespace types into separate header ...

sched/mmcid: Use proper data structures

2025-11-20T11:14:52Z

Having a lot of CID functionality specific members in struct task_struct and struct mm_struct is not really making the code easier to read. Encapsulate the CID specific parts in data structures and keep them separate from the stuff they are embedded in. No functional change. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Mathieu Desnoyers Link: https://patch.msgid.link/20251119172549.131573768@linutronix.de

ns: drop custom reference count initialization for initial namespaces

2025-11-11T09:01:32Z

Initial namespaces don't modify their reference count anymore. They remain fixed at one so drop the custom refcount initializations. Link: https://patch.msgid.link/20251110-work-namespace-nstree-fixes-v1-16-e8a9264e0fb9@kernel.org Signed-off-by: Christian Brauner

init: Replace simple_strtoul() with kstrtouint() in root_delay_setup()

2025-11-05T11:49:38Z

Replace deprecated simple_strtoul() with kstrtouint() for better error handling and input validation. Return 0 on parsing failure to indicate invalid parameter, maintaining existing behavior for valid inputs. The simple_strtoul() function is deprecated in favor of kstrtoint() family functions which provide better error handling and are recommended for new code and replacements. Signed-off-by: Kaushlendra Kumar Link: https://patch.msgid.link/20251103080627.1844645-1-kaushlendra.kumar@intel.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner

cred: make init_cred static

2025-11-04T11:36:02Z

There's zero need to expose struct init_cred. The very few places that need access can just go through init_task which is already exported. Link: https://patch.msgid.link/20251103-work-creds-init_cred-v1-3-cb3ec8711a6a@kernel.org Reviewed-by: Jens Axboe Signed-off-by: Christian Brauner

rseq: Switch to fast path processing on exit to user

2025-11-04T07:34:39Z

Now that all bits and pieces are in place, hook the RSEQ handling fast path function into exit_to_user_mode_prepare() after the TIF work bits have been handled. If case of fast path failure, TIF_NOTIFY_RESUME has been raised and the caller needs to take another turn through the TIF handling slow path. This only works for architectures which use the generic entry code. Architectures who still have their own incomplete hacks are not supported and won't be. This results in the following improvements: Kernel build Before After Reduction exit to user 80692981 80514451 signal checks: 32581 121 99% slowpath runs: 1201408 1.49% 198 0.00% 100% fastpath runs: 675941 0.84% N/A id updates: 1233989 1.53% 50541 0.06% 96% cs checks: 1125366 1.39% 0 0.00% 100% cs cleared: 1125366 100% 0 100% cs fixup: 0 0% 0 RSEQ selftests Before After Reduction exit to user: 386281778 387373750 signal checks: 35661203 0 100% slowpath runs: 140542396 36.38% 100 0.00% 100% fastpath runs: 9509789 2.51% N/A id updates: 176203599 45.62% 9087994 2.35% 95% cs checks: 175587856 45.46% 4728394 1.22% 98% cs cleared: 172359544 98.16% 1319307 27.90% 99% cs fixup: 3228312 1.84% 3409087 72.10% The 'cs cleared' and 'cs fixup' percentages are not relative to the exit to user invocations, they are relative to the actual 'cs check' invocations. While some of this could have been avoided in the original code, like the obvious clearing of CS when it's already clear, the main problem of going through TIF_NOTIFY_RESUME cannot be solved. In some workloads the RSEQ notify handler is invoked more than once before going out to user space. Doing this once when everything has stabilized is the only solution to avoid this. The initial attempt to completely decouple it from the TIF work turned out to be suboptimal for workloads, which do a lot of quick and short system calls. Even if the fast path decision is only 4 instructions (including a conditional branch), this adds up quickly and becomes measurable when the rate for actually having to handle rseq is in the low single digit percentage range of user/kernel transitions. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Mathieu Desnoyers Link: https://patch.msgid.link/20251027084307.701201365@linutronix.de

rseq: Provide static branch for runtime debugging

2025-11-04T07:32:49Z

Config based debug is rarely turned on and is not available easily when things go wrong. Provide a static branch to allow permanent integration of debug mechanisms along with the usual toggles in Kconfig, command line and debugfs. Requested-by: Peter Zijlstra Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Mathieu Desnoyers Link: https://patch.msgid.link/20251027084307.089270547@linutronix.de

rseq: Expose lightweight statistics in debugfs

2025-11-04T07:32:41Z

Analyzing the call frequency without actually using tracing is helpful for analysis of this infrastructure. The overhead is minimal as it just increments a per CPU counter associated to each operation. The debugfs readout provides a racy sum of all counters. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Mathieu Desnoyers Link: https://patch.msgid.link/20251027084307.027916598@linutronix.de