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srcutree: Warn if Tiny SRCU readers are preempted

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The fastpath of synchronize_srcu_atomic() should always be taken
because readers always disable preemption.  Therefore, the fact that
synchronize_srcu_atomic() is running at all should mean that all readers
have ended.

But there are always bugs.  And responding to a usage bug with a
too-short SRCU grace period, and thus possibly corrupting memory
is at best a sadistic response so such a bug.  For this reason,
synchronize_srcu_atomic() explicitly waits for readers.  Except that
it does so silently, possibly failing to flag this bug.  This commit
therefore adds a splat if synchronize_srcu_atomic() fails to take the
early exit.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2026-09-02 08:30:38 -07:00
parent f8d9588809
commit 494fa5fcb1
1 changed files with 8 additions and 0 deletions
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8
kernel/rcu/srcutiny.c
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@ -375,6 +375,14 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
return;
}
// Because readers disable preemption, we should never get here.
// However, a splat and some spinning is usually preferable to
// memory corruption due to a too-short grace period. There is
// the possibility that this will hang if the preempted reader is
// not looked upon favorably by the scheduler, but this is still
// preferable to memory corruption.
WARN_ON_ONCE(1);
// Wait to drive a grace period or for someone else to do it
// for us while we are lazily preempted.
while (ssp->srcu_atomic_gp_flag) {