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| author |   Uladzislau Rezki (Sony) <urezki@gmail.com> | 2024-02-14 14:45:53 -0800 |
|---|---|---|
| committer | Uladzislau Rezki (Sony) <urezki@gmail.com> | 2024-04-15 11:28:59 +0200 |
| commit | 058e87782c91696020bdb0aa28ddf77d89aed266 (patch) | |
| tree | fde9b02031a9697c2d3b60f732717c3bed246f25 | |
| parent | rcu: Add lockdep checks and kernel-doc header to rcu_softirq_qs() (diff) | |
| download | wireguard-linux-058e87782c91696020bdb0aa28ddf77d89aed266.tar.xz wireguard-linux-058e87782c91696020bdb0aa28ddf77d89aed266.zip | |
rcu: Update lockdep while in RCU read-side critical section
With Ankur's lazy-/auto-preemption patches applied and with a
lazy-preemptible kernel in combination with a non-preemptible RCU,
lockdep sometimes complains about context switches within RCU read-side
critical sections. This is a false positive due to rcu_read_unlock()
updating lockdep state too late:
__release(RCU);
__rcu_read_unlock();
// Context switch here results in lockdep false positive!!!
rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
Although this complaint could also happen with preemptible RCU
in a preemptible kernel, the odds of that happening aer quite low.
In constrast, with non-preemptible RCU, a long critical section has a
high probability of performing a context switch from the preempt_enable()
in __rcu_read_unlock().
The fix is straightforward, just move the rcu_lock_release()
within rcu_read_unlock() to obtain the reverse order from that of
rcu_read_lock():
rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
__release(RCU);
__rcu_read_unlock();
This commit makes this change.
Co-developed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Co-developed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to '')
| -rw-r--r-- | include/linux/rcupdate.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 17d7ed5f3ae6..2c54750e36a0 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -809,9 +809,9 @@ static inline void rcu_read_unlock(void) { RCU_LOCKDEP_WARN(!rcu_is_watching(), "rcu_read_unlock() used illegally while idle"); + rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ __release(RCU); __rcu_read_unlock(); - rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ } /** |