srcu: Make Tiny SRCU explicitly disable preemption

Because Tiny SRCU is used only in kernels built with either
CONFIG_PREEMPT_NONE=y or CONFIG_PREEMPT_VOLUNTARY=y, there has not
been any need for TINY SRCU to explicitly disable preemption.  However,
the prospect of lazy preemption changes that, and the lazy-preemption
patches do result in rcutorture runs finding both too-short grace periods
and grace-period hangs for Tiny SRCU.

This commit therefore adds the needed preempt_disable() and
preempt_enable() calls to Tiny SRCU.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 447133171d95fd859e5a16afa8ab4cf6104c3dbd..4d96bbdb45f086932cb595ce60814832e5aac3f2 100644 (file)
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -64,8 +64,10 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp)
 {
        int idx;
 
+       preempt_disable();  // Needed for PREEMPT_AUTO
        idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
        WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
+       preempt_enable();
        return idx;
 }
 

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index c38e5933a5d6937ce148d586f4023cd17e5bad30..5afd5cf494dba32a6e98e9cd376c362248a2c285 100644 (file)
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -96,9 +96,12 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
  */
 void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
 {
-       int newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
+       int newval;
 
+       preempt_disable();  // Needed for PREEMPT_AUTO
+       newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
        WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
+       preempt_enable();
        if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task())
                swake_up_one(&ssp->srcu_wq);
 }
@@ -117,8 +120,11 @@ void srcu_drive_gp(struct work_struct *wp)
        struct srcu_struct *ssp;
 
        ssp = container_of(wp, struct srcu_struct, srcu_work);
-       if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
+       preempt_disable();  // Needed for PREEMPT_AUTO
+       if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) {
                return; /* Already running or nothing to do. */
+               preempt_enable();
+       }
 
        /* Remove recently arrived callbacks and wait for readers. */
        WRITE_ONCE(ssp->srcu_gp_running, true);
@@ -130,9 +136,12 @@ void srcu_drive_gp(struct work_struct *wp)
        idx = (ssp->srcu_idx & 0x2) / 2;
        WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
        WRITE_ONCE(ssp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
+       preempt_enable();
        swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
+       preempt_disable();  // Needed for PREEMPT_AUTO
        WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
        WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
+       preempt_enable();
 
        /* Invoke the callbacks we removed above. */
        while (lh) {
@@ -150,8 +159,11 @@ void srcu_drive_gp(struct work_struct *wp)
         * at interrupt level, but the ->srcu_gp_running checks will
         * straighten that out.
         */
+       preempt_disable();  // Needed for PREEMPT_AUTO
        WRITE_ONCE(ssp->srcu_gp_running, false);
-       if (ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
+       idx = ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max));
+       preempt_enable();
+       if (idx)
                schedule_work(&ssp->srcu_work);
 }
 EXPORT_SYMBOL_GPL(srcu_drive_gp);
@@ -160,9 +172,12 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
 {
        unsigned long cookie;
 
+       preempt_disable();  // Needed for PREEMPT_AUTO
        cookie = get_state_synchronize_srcu(ssp);
-       if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie))
+       if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) {
+               preempt_enable();
                return;
+       }
        WRITE_ONCE(ssp->srcu_idx_max, cookie);
        if (!READ_ONCE(ssp->srcu_gp_running)) {
                if (likely(srcu_init_done))
@@ -170,6 +185,7 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
                else if (list_empty(&ssp->srcu_work.entry))
                        list_add(&ssp->srcu_work.entry, &srcu_boot_list);
        }
+       preempt_enable();
 }
 
 /*
@@ -183,11 +199,13 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 
        rhp->func = func;
        rhp->next = NULL;
+       preempt_disable();  // Needed for PREEMPT_AUTO
        local_irq_save(flags);
        *ssp->srcu_cb_tail = rhp;
        ssp->srcu_cb_tail = &rhp->next;
        local_irq_restore(flags);
        srcu_gp_start_if_needed(ssp);
+       preempt_enable();
 }
 EXPORT_SYMBOL_GPL(call_srcu);
 
@@ -241,9 +259,12 @@ EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
  */
 unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
 {
-       unsigned long ret = get_state_synchronize_srcu(ssp);
+       unsigned long ret;
 
+       preempt_disable();  // Needed for PREEMPT_AUTO
+       ret = get_state_synchronize_srcu(ssp);
        srcu_gp_start_if_needed(ssp);
+       preempt_enable();
        return ret;
 }
 EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);