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cgroup/cpuset: Change references of cpuset_mutex to cpuset_rwsem
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Since commit 1243dc5 ("cgroup/cpuset: Convert cpuset_mutex to
percpu_rwsem"), cpuset_mutex has been replaced by cpuset_rwsem which is
a percpu rwsem. However, the comments in kernel/cgroup/cpuset.c still
reference cpuset_mutex which are now incorrect.

Change all the references of cpuset_mutex to cpuset_rwsem.

Fixes: 1243dc5 ("cgroup/cpuset: Convert cpuset_mutex to percpu_rwsem")
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
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@Waiman-Long @htejun
Waiman-Long authored and htejun committed Sep 13, 2021
1 parent 22b1255 commit b94f9ac
Showing 1 changed file with 29 additions and 27 deletions.
56 changes: 29 additions & 27 deletions kernel/cgroup/cpuset.c
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Original file line number Diff line number Diff line change
Expand Up @@ -311,17 +311,19 @@ static struct cpuset top_cpuset = {
if (is_cpuset_online(((des_cs) = css_cs((pos_css)))))

/*
* There are two global locks guarding cpuset structures - cpuset_mutex and
* There are two global locks guarding cpuset structures - cpuset_rwsem and
* callback_lock. We also require taking task_lock() when dereferencing a
* task's cpuset pointer. See "The task_lock() exception", at the end of this
* comment.
* comment. The cpuset code uses only cpuset_rwsem write lock. Other
* kernel subsystems can use cpuset_read_lock()/cpuset_read_unlock() to
* prevent change to cpuset structures.
*
* A task must hold both locks to modify cpusets. If a task holds
* cpuset_mutex, then it blocks others wanting that mutex, ensuring that it
* cpuset_rwsem, it blocks others wanting that rwsem, ensuring that it
* is the only task able to also acquire callback_lock and be able to
* modify cpusets. It can perform various checks on the cpuset structure
* first, knowing nothing will change. It can also allocate memory while
* just holding cpuset_mutex. While it is performing these checks, various
* just holding cpuset_rwsem. While it is performing these checks, various
* callback routines can briefly acquire callback_lock to query cpusets.
* Once it is ready to make the changes, it takes callback_lock, blocking
* everyone else.
Expand Down Expand Up @@ -393,7 +395,7 @@ static inline bool is_in_v2_mode(void)
* One way or another, we guarantee to return some non-empty subset
* of cpu_online_mask.
*
* Call with callback_lock or cpuset_mutex held.
* Call with callback_lock or cpuset_rwsem held.
*/
static void guarantee_online_cpus(struct task_struct *tsk,
struct cpumask *pmask)
Expand Down Expand Up @@ -435,7 +437,7 @@ static void guarantee_online_cpus(struct task_struct *tsk,
* One way or another, we guarantee to return some non-empty subset
* of node_states[N_MEMORY].
*
* Call with callback_lock or cpuset_mutex held.
* Call with callback_lock or cpuset_rwsem held.
*/
static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
{
Expand All @@ -447,7 +449,7 @@ static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
/*
* update task's spread flag if cpuset's page/slab spread flag is set
*
* Call with callback_lock or cpuset_mutex held.
* Call with callback_lock or cpuset_rwsem held.
*/
static void cpuset_update_task_spread_flag(struct cpuset *cs,
struct task_struct *tsk)
Expand All @@ -468,7 +470,7 @@ static void cpuset_update_task_spread_flag(struct cpuset *cs,
*
* One cpuset is a subset of another if all its allowed CPUs and
* Memory Nodes are a subset of the other, and its exclusive flags
* are only set if the other's are set. Call holding cpuset_mutex.
* are only set if the other's are set. Call holding cpuset_rwsem.
*/

static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
Expand Down Expand Up @@ -577,7 +579,7 @@ static inline void free_cpuset(struct cpuset *cs)
* If we replaced the flag and mask values of the current cpuset
* (cur) with those values in the trial cpuset (trial), would
* our various subset and exclusive rules still be valid? Presumes
* cpuset_mutex held.
* cpuset_rwsem held.
*
* 'cur' is the address of an actual, in-use cpuset. Operations
* such as list traversal that depend on the actual address of the
Expand Down Expand Up @@ -700,7 +702,7 @@ static void update_domain_attr_tree(struct sched_domain_attr *dattr,
rcu_read_unlock();
}

/* Must be called with cpuset_mutex held. */
/* Must be called with cpuset_rwsem held. */
static inline int nr_cpusets(void)
{
/* jump label reference count + the top-level cpuset */
Expand All @@ -726,7 +728,7 @@ static inline int nr_cpusets(void)
* domains when operating in the severe memory shortage situations
* that could cause allocation failures below.
*
* Must be called with cpuset_mutex held.
* Must be called with cpuset_rwsem held.
*
* The three key local variables below are:
* cp - cpuset pointer, used (together with pos_css) to perform a
Expand Down Expand Up @@ -1005,7 +1007,7 @@ partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
* 'cpus' is removed, then call this routine to rebuild the
* scheduler's dynamic sched domains.
*
* Call with cpuset_mutex held. Takes cpus_read_lock().
* Call with cpuset_rwsem held. Takes cpus_read_lock().
*/
static void rebuild_sched_domains_locked(void)
{
Expand Down Expand Up @@ -1078,7 +1080,7 @@ void rebuild_sched_domains(void)
* @cs: the cpuset in which each task's cpus_allowed mask needs to be changed
*
* Iterate through each task of @cs updating its cpus_allowed to the
* effective cpuset's. As this function is called with cpuset_mutex held,
* effective cpuset's. As this function is called with cpuset_rwsem held,
* cpuset membership stays stable.
*/
static void update_tasks_cpumask(struct cpuset *cs)
Expand Down Expand Up @@ -1347,7 +1349,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cpuset, int cmd,
*
* On legacy hierarchy, effective_cpus will be the same with cpu_allowed.
*
* Called with cpuset_mutex held
* Called with cpuset_rwsem held
*/
static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp)
{
Expand Down Expand Up @@ -1704,12 +1706,12 @@ static void *cpuset_being_rebound;
* @cs: the cpuset in which each task's mems_allowed mask needs to be changed
*
* Iterate through each task of @cs updating its mems_allowed to the
* effective cpuset's. As this function is called with cpuset_mutex held,
* effective cpuset's. As this function is called with cpuset_rwsem held,
* cpuset membership stays stable.
*/
static void update_tasks_nodemask(struct cpuset *cs)
{
static nodemask_t newmems; /* protected by cpuset_mutex */
static nodemask_t newmems; /* protected by cpuset_rwsem */
struct css_task_iter it;
struct task_struct *task;

Expand All @@ -1722,7 +1724,7 @@ static void update_tasks_nodemask(struct cpuset *cs)
* take while holding tasklist_lock. Forks can happen - the
* mpol_dup() cpuset_being_rebound check will catch such forks,
* and rebind their vma mempolicies too. Because we still hold
* the global cpuset_mutex, we know that no other rebind effort
* the global cpuset_rwsem, we know that no other rebind effort
* will be contending for the global variable cpuset_being_rebound.
* It's ok if we rebind the same mm twice; mpol_rebind_mm()
* is idempotent. Also migrate pages in each mm to new nodes.
Expand Down Expand Up @@ -1768,7 +1770,7 @@ static void update_tasks_nodemask(struct cpuset *cs)
*
* On legacy hierarchy, effective_mems will be the same with mems_allowed.
*
* Called with cpuset_mutex held
* Called with cpuset_rwsem held
*/
static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
{
Expand Down Expand Up @@ -1821,7 +1823,7 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
* mempolicies and if the cpuset is marked 'memory_migrate',
* migrate the tasks pages to the new memory.
*
* Call with cpuset_mutex held. May take callback_lock during call.
* Call with cpuset_rwsem held. May take callback_lock during call.
* Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
* lock each such tasks mm->mmap_lock, scan its vma's and rebind
* their mempolicies to the cpusets new mems_allowed.
Expand Down Expand Up @@ -1911,7 +1913,7 @@ static int update_relax_domain_level(struct cpuset *cs, s64 val)
* @cs: the cpuset in which each task's spread flags needs to be changed
*
* Iterate through each task of @cs updating its spread flags. As this
* function is called with cpuset_mutex held, cpuset membership stays
* function is called with cpuset_rwsem held, cpuset membership stays
* stable.
*/
static void update_tasks_flags(struct cpuset *cs)
Expand All @@ -1931,7 +1933,7 @@ static void update_tasks_flags(struct cpuset *cs)
* cs: the cpuset to update
* turning_on: whether the flag is being set or cleared
*
* Call with cpuset_mutex held.
* Call with cpuset_rwsem held.
*/

static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
Expand Down Expand Up @@ -1980,7 +1982,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
* cs: the cpuset to update
* new_prs: new partition root state
*
* Call with cpuset_mutex held.
* Call with cpuset_rwsem held.
*/
static int update_prstate(struct cpuset *cs, int new_prs)
{
Expand Down Expand Up @@ -2167,7 +2169,7 @@ static int fmeter_getrate(struct fmeter *fmp)

static struct cpuset *cpuset_attach_old_cs;

/* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
/* Called by cgroups to determine if a cpuset is usable; cpuset_rwsem held */
static int cpuset_can_attach(struct cgroup_taskset *tset)
{
struct cgroup_subsys_state *css;
Expand Down Expand Up @@ -2219,15 +2221,15 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)
}

/*
* Protected by cpuset_mutex. cpus_attach is used only by cpuset_attach()
* Protected by cpuset_rwsem. cpus_attach is used only by cpuset_attach()
* but we can't allocate it dynamically there. Define it global and
* allocate from cpuset_init().
*/
static cpumask_var_t cpus_attach;

static void cpuset_attach(struct cgroup_taskset *tset)
{
/* static buf protected by cpuset_mutex */
/* static buf protected by cpuset_rwsem */
static nodemask_t cpuset_attach_nodemask_to;
struct task_struct *task;
struct task_struct *leader;
Expand Down Expand Up @@ -2417,7 +2419,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
* operation like this one can lead to a deadlock through kernfs
* active_ref protection. Let's break the protection. Losing the
* protection is okay as we check whether @cs is online after
* grabbing cpuset_mutex anyway. This only happens on the legacy
* grabbing cpuset_rwsem anyway. This only happens on the legacy
* hierarchies.
*/
css_get(&cs->css);
Expand Down Expand Up @@ -3672,7 +3674,7 @@ void __cpuset_memory_pressure_bump(void)
* - Used for /proc/<pid>/cpuset.
* - No need to task_lock(tsk) on this tsk->cpuset reference, as it
* doesn't really matter if tsk->cpuset changes after we read it,
* and we take cpuset_mutex, keeping cpuset_attach() from changing it
* and we take cpuset_rwsem, keeping cpuset_attach() from changing it
* anyway.
*/
int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
Expand Down

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