Commit 8b82c18b authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'sched-urgent-2025-02-22' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull rseq fixes from Ingo Molnar:

 - Fix overly spread-out RSEQ concurrency ID allocation pattern that
   regressed certain workloads

 - Fix RSEQ registration syscall behavior on -EFAULT errors when
   CONFIG_DEBUG_RSEQ=y (This debug option is disabled on most
   distributions)

* tag 'sched-urgent-2025-02-22' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  rseq: Fix rseq registration with CONFIG_DEBUG_RSEQ
  sched: Compact RSEQ concurrency IDs with reduced threads and affinity
parents 1ceffff6 dc0a241c

include/linux/mm_types.h

+4 −3
Original line number Diff line number Diff line
@@ -875,10 +875,11 @@ struct mm_struct { 
		 */

		unsigned int nr_cpus_allowed;

		/**

		 * @max_nr_cid: Maximum number of concurrency IDs allocated.

		 * @max_nr_cid: Maximum number of allowed concurrency

		 *              IDs allocated.

		 *

		 * Track the highest number of concurrency IDs allocated for the

		 * mm.

		 * Track the highest number of allowed concurrency IDs

		 * allocated for the mm.

		 */

		atomic_t max_nr_cid;

		/**

kernel/rseq.c

+8 −3
Original line number Diff line number Diff line
@@ -507,9 +507,6 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, 
		return -EINVAL;

	if (!access_ok(rseq, rseq_len))

		return -EFAULT;

	current->rseq = rseq;

	current->rseq_len = rseq_len;

	current->rseq_sig = sig;

#ifdef CONFIG_DEBUG_RSEQ

	/*

	 * Initialize the in-kernel rseq fields copy for validation of
@@ -521,6 +518,14 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, 
	    get_user(rseq_kernel_fields(current)->mm_cid, &rseq->mm_cid))

		return -EFAULT;

#endif

	/*

	 * Activate the registration by setting the rseq area address, length

	 * and signature in the task struct.

	 */

	current->rseq = rseq;

	current->rseq_len = rseq_len;

	current->rseq_sig = sig;



	/*

	 * If rseq was previously inactive, and has just been

	 * registered, ensure the cpu_id_start and cpu_id fields

kernel/sched/sched.h

+22 −3
Original line number Diff line number Diff line
@@ -3698,10 +3698,28 @@ static inline int __mm_cid_try_get(struct task_struct *t, struct mm_struct *mm) 
{

	struct cpumask *cidmask = mm_cidmask(mm);

	struct mm_cid __percpu *pcpu_cid = mm->pcpu_cid;

	int cid = __this_cpu_read(pcpu_cid->recent_cid);

	int cid, max_nr_cid, allowed_max_nr_cid;



	/*

	 * After shrinking the number of threads or reducing the number

	 * of allowed cpus, reduce the value of max_nr_cid so expansion

	 * of cid allocation will preserve cache locality if the number

	 * of threads or allowed cpus increase again.

	 */

	max_nr_cid = atomic_read(&mm->max_nr_cid);

	while ((allowed_max_nr_cid = min_t(int, READ_ONCE(mm->nr_cpus_allowed),

					   atomic_read(&mm->mm_users))),

	       max_nr_cid > allowed_max_nr_cid) {

		/* atomic_try_cmpxchg loads previous mm->max_nr_cid into max_nr_cid. */

		if (atomic_try_cmpxchg(&mm->max_nr_cid, &max_nr_cid, allowed_max_nr_cid)) {

			max_nr_cid = allowed_max_nr_cid;

			break;

		}

	}

	/* Try to re-use recent cid. This improves cache locality. */

	if (!mm_cid_is_unset(cid) && !cpumask_test_and_set_cpu(cid, cidmask))

	cid = __this_cpu_read(pcpu_cid->recent_cid);

	if (!mm_cid_is_unset(cid) && cid < max_nr_cid &&

	    !cpumask_test_and_set_cpu(cid, cidmask))

		return cid;

	/*

	 * Expand cid allocation if the maximum number of concurrency
@@ -3709,8 +3727,9 @@ static inline int __mm_cid_try_get(struct task_struct *t, struct mm_struct *mm) 
	 * and number of threads. Expanding cid allocation as much as

	 * possible improves cache locality.

	 */

	cid = atomic_read(&mm->max_nr_cid);

	cid = max_nr_cid;

	while (cid < READ_ONCE(mm->nr_cpus_allowed) && cid < atomic_read(&mm->mm_users)) {

		/* atomic_try_cmpxchg loads previous mm->max_nr_cid into cid. */

		if (!atomic_try_cmpxchg(&mm->max_nr_cid, &cid, cid + 1))

			continue;

		if (!cpumask_test_and_set_cpu(cid, cidmask))