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srcu: Permit Tiny SRCU srcu_read_unlock() with interrupts disabled

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The current Tiny SRCU implementation of srcu_read_unlock() awakens
the grace-period processing when exiting the outermost SRCU read-side
critical section.  However, not all Linux-kernel configurations and
contexts permit swake_up_one() to be invoked while interrupts are
disabled, and this can result in indefinitely extended SRCU grace periods.
This commit therefore only invokes swake_up_one() when interrupts are
enabled, and introduces polling to the grace-period workqueue handler.

Reported-by: kernel test robot <oliver.sang@intel.com>
Reported-by: Zqiang <qiang.zhang@linux.dev>
Closes: https://lore.kernel.org/oe-lkp/202508261642.b15eefbb-lkp@intel.com
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit is contained in:
Paul E. McKenney 2025-11-05 12:32:01 -08:00 • committed by Frederic Weisbecker
parent 3a86608788
commit 58ac42f278
1 changed files with 9 additions and 4 deletions
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13
kernel/rcu/srcutiny.c
View file

@ -106,15 +106,15 @@ void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
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())
if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task() && !irqs_disabled())
swake_up_one(&ssp->srcu_wq);
}
EXPORT_SYMBOL_GPL(__srcu_read_unlock);
/*
* Workqueue handler to drive one grace period and invoke any callbacks
* that become ready as a result. Single-CPU and !PREEMPTION operation
* means that we get away with murder on synchronization. ;-)
* that become ready as a result. Single-CPU operation and preemption
* disabling mean that we get away with murder on synchronization. ;-)
*/
void srcu_drive_gp(struct work_struct *wp)
{
@ -141,7 +141,12 @@ void srcu_drive_gp(struct work_struct *wp)
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]));
do {
// Deadlock issues prevent __srcu_read_unlock() from
// doing an unconditional wakeup, so polling is required.
swait_event_timeout_exclusive(ssp->srcu_wq,
!READ_ONCE(ssp->srcu_lock_nesting[idx]), HZ / 10);
} while (READ_ONCE(ssp->srcu_lock_nesting[idx]));
preempt_disable(); // Needed for PREEMPT_LAZY
WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);