Signed-off-by: Waiman Long <[email protected]>
---
kernel/cgroup/cpuset.c | 79 ++++++++++++++++++++++++-----------
kernel/sched/isolation.c | 4 +-
kernel/time/timer_migration.c | 3 +-
3 files changed, 57 insertions(+), 29 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 98c7cb732206..96390ceb5122 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -78,7 +78,7 @@ static cpumask_var_t subpartitions_cpus;
static cpumask_var_t isolated_cpus;
/*
- * isolated_cpus updating flag (protected by cpuset_mutex)
+ * isolated_cpus updating flag (protected by isolcpus_update_mutex)
* Set if isolated_cpus is going to be updated in the current
* cpuset_mutex crtical section.
*/
@@ -223,29 +223,46 @@ struct cpuset top_cpuset = {
};
/*
- * There are two global locks guarding cpuset structures - cpuset_mutex and
- * callback_lock. The cpuset code uses only cpuset_mutex. Other kernel
- * subsystems can use cpuset_lock()/cpuset_unlock() to prevent change to cpuset
- * structures. Note that cpuset_mutex needs to be a mutex as it is used in
- * paths that rely on priority inheritance (e.g. scheduler - on RT) for
- * correctness.
+ * CPUSET Locking Convention
+ * -------------------------
*
- * A task must hold both locks to modify cpusets. If a task holds
- * cpuset_mutex, it blocks others, 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 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.
+ * Below are the three global locks guarding cpuset structures in lock
+ * acquisition order:
+ * - isolcpus_update_mutex (optional)
+ * - cpu_hotplug_lock (cpus_read_lock/cpus_write_lock)
+ * - cpuset_mutex
+ * - callback_lock (raw spinlock)
*
- * Calls to the kernel memory allocator can not be made while holding
- * callback_lock, as that would risk double tripping on callback_lock
- * from one of the callbacks into the cpuset code from within
- * __alloc_pages().
+ * The first isolcpus_update_mutex should only be held if the existing set of
+ * isolated CPUs (in isolated partition) or any of the partition states may be
+ * changed when some cpuset control files are being written into. Otherwise,
+ * it can be skipped. Holding isolcpus_update_mutex/cpus_read_lock or
+ * cpus_write_lock will ensure mutual exclusion of isolated_cpus update.
*
- * If a task is only holding callback_lock, then it has read-only
- * access to cpusets.
+ * As cpuset will now indirectly flush a number of different workqueues in
+ * housekeeping_update() when the set of isolated CPUs is going to be changed,
+ * it may not be safe from the circular locking perspective to hold the
+ * cpus_read_lock. So cpuset_full_lock() will be released before calling
+ * housekeeping_update() and re-acquired afterward.
+ *
+ * A task must hold all the remaining three locks to modify externally visible
+ * or used fields of cpusets, though some of the internally used cpuset fields
+ * can be modified by holding cpu_hotplug_lock and cpuset_mutex only. If only
+ * reliable read access of the externally used fields are needed, a task can
+ * hold either cpuset_mutex or callback_lock.
+ *
+ * If a task holds cpu_hotplug_lock and cpuset_mutex, it blocks others,
+ * 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
+ * without holding callback_lock. 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.
+ *
+ * Calls to the kernel memory allocator cannot be made while holding
+ * callback_lock which is a spinlock, as the memory allocator may sleep or
+ * call back into cpuset code and acquire callback_lock.
*
* Now, the task_struct fields mems_allowed and mempolicy may be changed
* by other task, we use alloc_lock in the task_struct fields to protect
@@ -256,6 +273,7 @@ struct cpuset top_cpuset = {
* cpumasks and nodemasks.
*/
+static DEFINE_MUTEX(isolcpus_update_mutex);
static DEFINE_MUTEX(cpuset_mutex);
/**
@@ -302,7 +320,7 @@ void cpuset_full_unlock(void)
#ifdef CONFIG_LOCKDEP
bool lockdep_is_cpuset_held(void)
{
- return lockdep_is_held(&cpuset_mutex);
+ return lockdep_is_held(&isolcpus_update_mutex);
}
#endif
@@ -1294,9 +1312,8 @@ static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus)
static void __update_isolation_cpumasks(bool twork);
static void isolation_task_work_fn(struct callback_head *cb)
{
- cpuset_full_lock();
+ guard(mutex)(&isolcpus_update_mutex);
__update_isolation_cpumasks(true);
- cpuset_full_lock();
}
/*
@@ -1338,8 +1355,18 @@ static void __update_isolation_cpumasks(bool twork)
return;
}
+ lockdep_assert_held(&isolcpus_update_mutex);
+ /*
+ * Release cpus_read_lock & cpuset_mutex before calling
+ * housekeeping_update() and re-acquiring them afterward if not
+ * calling from task_work.
+ */
+ if (!twork)
+ cpuset_full_unlock();
ret = housekeeping_update(isolated_cpus);
WARN_ON_ONCE(ret < 0);
+ if (!twork)
+ cpuset_full_lock();
isolated_cpus_updating = false;
}
@@ -3196,6 +3223,7 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
return -EACCES;
buf = strstrip(buf);
+ mutex_lock(&isolcpus_update_mutex);
cpuset_full_lock();
if (!is_cpuset_online(cs))
goto out_unlock;
@@ -3226,6 +3254,7 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
rebuild_sched_domains_locked();
out_unlock:
cpuset_full_unlock();
+ mutex_unlock(&isolcpus_update_mutex);
if (of_cft(of)->private == FILE_MEMLIST)
schedule_flush_migrate_mm();
return retval ?: nbytes;
@@ -3329,6 +3358,7 @@ static ssize_t cpuset_partition_write(struct
kernfs_open_file *of, char *buf,
else
return -EINVAL;
+ guard(mutex)(&isolcpus_update_mutex);
cpuset_full_lock();
if (is_cpuset_online(cs))
retval = update_prstate(cs, val);
@@ -3502,6 +3532,7 @@ static void cpuset_css_killed(struct cgroup_subsys_state
*css)
{
struct cpuset *cs = css_cs(css);
+ guard(mutex)(&isolcpus_update_mutex);
cpuset_full_lock();
/* Reset valid partition back to member */
if (is_partition_valid(cs))
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 3b725d39c06e..ef152d401fe2 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -123,8 +123,6 @@ int housekeeping_update(struct cpumask *isol_mask)
struct cpumask *trial, *old = NULL;
int err;
- lockdep_assert_cpus_held();
-
trial = kmalloc(cpumask_size(), GFP_KERNEL);
if (!trial)
return -ENOMEM;
@@ -136,7 +134,7 @@ int housekeeping_update(struct cpumask *isol_mask)
}
if (!housekeeping.flags)
- static_branch_enable_cpuslocked(&housekeeping_overridden);
+ static_branch_enable(&housekeeping_overridden);
if (housekeeping.flags & HK_FLAG_DOMAIN)
old = housekeeping_cpumask_dereference(HK_TYPE_DOMAIN);
diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
index 6da9cd562b20..244a8d025e78 100644
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -1559,8 +1559,6 @@ int tmigr_isolated_exclude_cpumask(struct cpumask
*exclude_cpumask)
cpumask_var_t cpumask __free(free_cpumask_var) = CPUMASK_VAR_NULL;
int cpu;
- lockdep_assert_cpus_held();
-
if (!works)
return -ENOMEM;
if (!alloc_cpumask_var(&cpumask, GFP_KERNEL))
@@ -1570,6 +1568,7 @@ int tmigr_isolated_exclude_cpumask(struct cpumask
*exclude_cpumask)
* First set previously isolated CPUs as available (unisolate).
* This cpumask contains only CPUs that switched to available now.
*/
+ guard(cpus_read_lock)();
cpumask_andnot(cpumask, cpu_online_mask, exclude_cpumask);
cpumask_andnot(cpumask, cpumask, tmigr_available_cpumask);
