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srcu: Restrict atomic-SRCU non_block annotation to task context

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srcu_read_lock_atomic() and srcu_read_unlock_atomic() arm and disarm
might_sleep() checks via non_block_start()/non_block_end(), skipping
hardirq so the update does not land on the interrupted task's
->non_block_count.

Inline softirqs run on the interrupted task's stack as well, so a
timer callback running atomic-SRCU readers races with the interrupted
task's own ->non_block_count updates, as KCSAN reports:

	BUG: KCSAN: data-race in srcu_torture_read_lock / srcu_torture_read_unlock

	write to 0xffffa00f818ea418 of 4 bytes by interrupt on cpu 0:
		srcu_torture_read_lock+0x422/0x470
		rcutorture_one_extend+0xdc/0x600
		rcu_torture_one_read+0xd1/0x330
		rcu_torture_timer+0x75/0x140
		call_timer_fn+0xe6/0x2f0
		...
		run_timer_softirq+0xb7/0x130
		handle_softirqs+0xfc/0x3f0
		__irq_exit_rcu+0x8e/0x100

Use in_task() so the annotation is applied only in task context; it
is redundant elsewhere because might_sleep() already warns about
sleeping from atomic context.

Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Kunwu Chan 2026-09-07 15:58:29 +08:00 committed by Paul E. McKenney
parent 47138812bc
commit cc7287f9ee
1 changed files with 6 additions and 4 deletions
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10
include/linux/srcu.h
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@ -346,11 +346,13 @@ static inline int srcu_read_lock_atomic(struct srcu_struct *ssp)
/*
* Arm might_sleep() to catch even a *potentially* sleeping call
* in the section, not just an actual schedule: the atomic-domain
* promise must hold on every path, contended or not. In hardirq
* the annotation would land on the interrupted task; it is also
* promise must hold on every path, contended or not. In hardirq,
* softirq, or NMI the annotation would land on the interrupted
* task, and can also result in data races against that task's
* own non_block_start()/non_block_end() invocations; it is also
* redundant there, so skip it.
*/
if (!in_hardirq())
if (in_task())
non_block_start();
srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_ATOMIC);
retval = __srcu_read_lock(ssp);
@ -562,7 +564,7 @@ static inline void srcu_read_unlock_atomic(struct srcu_struct *ssp, int idx)
srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_ATOMIC);
srcu_lock_release(&ssp->dep_map);
__srcu_read_unlock(ssp, idx);
if (!in_hardirq())
if (in_task())
non_block_end();
preempt_enable();
}