sched: tasks: Use sequence counter with associated spinlock

A sequence counter write side critical section must be protected by some
form of locking to serialize writers. A plain seqcount_t does not
contain the information of which lock must be held when entering a write
side critical section.

Use the new seqcount_spinlock_t data type, which allows to associate a
spinlock with the sequence counter. This enables lockdep to verify that
the spinlock used for writer serialization is held when the write side
critical section is entered.

If lockdep is disabled this lock association is compiled out and has
neither storage size nor runtime overhead.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-14-a.darwish@linutronix.de

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8d1de02..9a9d826 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1050,7 +1050,7 @@ struct task_struct {
        /* Protected by ->alloc_lock: */
        nodemask_t                      mems_allowed;
        /* Seqence number to catch updates: */
-       seqcount_t                      mems_allowed_seq;
+       seqcount_spinlock_t             mems_allowed_seq;
        int                             cpuset_mem_spread_rotor;
        int                             cpuset_slab_spread_rotor;
 #endif

diff --git a/init/init_task.c b/init/init_task.c
index 15089d1..94fe3ba 100644 (file)
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -154,7 +154,8 @@ struct task_struct init_task
        .trc_holdout_list = LIST_HEAD_INIT(init_task.trc_holdout_list),
 #endif
 #ifdef CONFIG_CPUSETS
-       .mems_allowed_seq = SEQCNT_ZERO(init_task.mems_allowed_seq),
+       .mems_allowed_seq = SEQCNT_SPINLOCK_ZERO(init_task.mems_allowed_seq,
+                                                &init_task.alloc_lock),
 #endif
 #ifdef CONFIG_RT_MUTEXES
        .pi_waiters     = RB_ROOT_CACHED,

diff --git a/kernel/fork.c b/kernel/fork.c
index 70d9d0a..fc72f09 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2032,7 +2032,7 @@ static __latent_entropy struct task_struct *copy_process(
 #ifdef CONFIG_CPUSETS
        p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
        p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
-       seqcount_init(&p->mems_allowed_seq);
+       seqcount_spinlock_init(&p->mems_allowed_seq, &p->alloc_lock);
 #endif
 #ifdef CONFIG_TRACE_IRQFLAGS
        p->irq_events = 0;