Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | From | Yury Norov <> | Subject | [PATCH v3 05/35] sched: add cpumask_find_and_set() and use it in __mm_cid_get() | Date | Mon, 11 Dec 2023 18:27:19 -0800 |
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__mm_cid_get() uses __mm_cid_try_get() helper to atomically acquire a bit in mm cid mask. Now that we have atomic find_and_set_bit(), we can easily extend it to cpumasks and use in the scheduler code.
cpumask_find_and_set() considers cid mask as a volatile region of memory, as it actually is in this case. So, if it's changed while search is in progress, KCSAN wouldn't fire warning on it.
CC: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> CC: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Yury Norov <yury.norov@gmail.com> --- include/linux/cpumask.h | 12 ++++++++++++ kernel/sched/sched.h | 14 +++++--------- 2 files changed, 17 insertions(+), 9 deletions(-)
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h index cfb545841a2c..c2acced8be4e 100644 --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -271,6 +271,18 @@ unsigned int cpumask_next_and(int n, const struct cpumask *src1p, small_cpumask_bits, n + 1); } +/** + * cpumask_find_and_set - find the first unset cpu in a cpumask and + * set it atomically + * @srcp: the cpumask pointer + * + * Return: >= nr_cpu_ids if nothing is found. + */ +static inline unsigned int cpumask_find_and_set(volatile struct cpumask *srcp) +{ + return find_and_set_bit(cpumask_bits(srcp), small_cpumask_bits); +} + /** * for_each_cpu - iterate over every cpu in a mask * @cpu: the (optionally unsigned) integer iterator diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 2e5a95486a42..2ce9112de89b 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -3347,23 +3347,19 @@ static inline void mm_cid_put(struct mm_struct *mm) static inline int __mm_cid_try_get(struct mm_struct *mm) { - struct cpumask *cpumask; - int cid; + struct cpumask *cpumask = mm_cidmask(mm); + int cid = nr_cpu_ids; - cpumask = mm_cidmask(mm); /* * Retry finding first zero bit if the mask is temporarily * filled. This only happens during concurrent remote-clear * which owns a cid without holding a rq lock. */ - for (;;) { - cid = cpumask_first_zero(cpumask); - if (cid < nr_cpu_ids) - break; + while (cid >= nr_cpu_ids) { + cid = cpumask_find_and_set(cpumask); cpu_relax(); } - if (cpumask_test_and_set_cpu(cid, cpumask)) - return -1; + return cid; } -- 2.40.1
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