cpuset: refactor CPU mask buffer parsing logic

The current implementation contains redundant handling for empty mask
inputs, as cpulist_parse() already properly handles these cases. This
refactoring introduces a new helper function parse_cpuset_cpulist() to
consolidate CPU list parsing logic and eliminate special-case checks for
empty inputs.

Additionally, the effective_xcpus computation for trial cpusets has been
simplified. Rather than computing effective_xcpus only when exclusive_cpus
is set or when the cpuset forms a valid partition, we now recalculate it
on every cpuset.cpus update. This approach ensures consistency and allows
removal of redundant effective_xcpus logic in subsequent patches.

The trial cpuset's effective_xcpus calculation follows two distinct cases:
1. For member cpusets: effective_xcpus is determined by the intersection
   of cpuset->exclusive_cpus and the parent's effective_xcpus.
2. For non-member cpusets: effective_xcpus is derived from the intersection
   of user_xcpus and the parent's effective_xcpus.

Signed-off-by: Chen Ridong <chenridong@huawei.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 2b87a4b09fc95330dd06502a8d61bbf56aad8038..45784c62d1c698e00d768857ad691e24c378131f 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -170,6 +170,11 @@ static inline bool is_partition_invalid(const struct cpuset *cs)
        return cs->partition_root_state < 0;
 }
 
+static inline bool cs_is_member(const struct cpuset *cs)
+{
+       return cs->partition_root_state == PRS_MEMBER;
+}
+
 /*
  * Callers should hold callback_lock to modify partition_root_state.
  */
@@ -1479,7 +1484,13 @@ static int compute_trialcs_excpus(struct cpuset *trialcs, struct cpuset *cs)
        struct cpuset *parent = parent_cs(trialcs);
        struct cpumask *excpus = trialcs->effective_xcpus;
 
-       cpumask_and(excpus, user_xcpus(trialcs), parent->effective_xcpus);
+       /* trialcs is member, cpuset.cpus has no impact to excpus */
+       if (cs_is_member(cs))
+               cpumask_and(excpus, trialcs->exclusive_cpus,
+                               parent->effective_xcpus);
+       else
+               cpumask_and(excpus, user_xcpus(trialcs), parent->effective_xcpus);
+
        return rm_siblings_excl_cpus(parent, cs, excpus);
 }
 
@@ -2349,6 +2360,19 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
        rcu_read_unlock();
 }
 
+static int parse_cpuset_cpulist(const char *buf, struct cpumask *out_mask)
+{
+       int retval;
+
+       retval = cpulist_parse(buf, out_mask);
+       if (retval < 0)
+               return retval;
+       if (!cpumask_subset(out_mask, top_cpuset.cpus_allowed))
+               return -EINVAL;
+
+       return 0;
+}
+
 /**
  * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
  * @cs: the cpuset to consider
@@ -2365,34 +2389,9 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
        bool force = false;
        int old_prs = cs->partition_root_state;
 
-       /*
-        * An empty cpus_allowed is ok only if the cpuset has no tasks.
-        * Since cpulist_parse() fails on an empty mask, we special case
-        * that parsing.  The validate_change() call ensures that cpusets
-        * with tasks have cpus.
-        */
-       if (!*buf) {
-               cpumask_clear(trialcs->cpus_allowed);
-               if (cpumask_empty(trialcs->exclusive_cpus))
-                       cpumask_clear(trialcs->effective_xcpus);
-       } else {
-               retval = cpulist_parse(buf, trialcs->cpus_allowed);
-               if (retval < 0)
-                       return retval;
-
-               if (!cpumask_subset(trialcs->cpus_allowed,
-                                   top_cpuset.cpus_allowed))
-                       return -EINVAL;
-
-               /*
-                * When exclusive_cpus isn't explicitly set, it is constrained
-                * by cpus_allowed and parent's effective_xcpus. Otherwise,
-                * trialcs->effective_xcpus is used as a temporary cpumask
-                * for checking validity of the partition root.
-                */
-               if (!cpumask_empty(trialcs->exclusive_cpus) || is_partition_valid(cs))
-                       compute_trialcs_excpus(trialcs, cs);
-       }
+       retval = parse_cpuset_cpulist(buf, trialcs->cpus_allowed);
+       if (retval < 0)
+               return retval;
 
        /* Nothing to do if the cpus didn't change */
        if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
@@ -2401,6 +2400,8 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
        if (alloc_tmpmasks(&tmp))
                return -ENOMEM;
 
+       compute_trialcs_excpus(trialcs, cs);
+
        if (old_prs) {
                if (is_partition_valid(cs) &&
                    cpumask_empty(trialcs->effective_xcpus)) {