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author | Dmitry Torokhov <dmitry.torokhov@gmail.com> | 2012-04-22 06:28:35 (GMT) |
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committer | Dmitry Torokhov <dmitry.torokhov@gmail.com> | 2012-04-22 06:28:35 (GMT) |
commit | 57b8628bb0ac4e47c806e45c5bbd89282e93869b (patch) | |
tree | ee9289f0898054474b7e5054abdb3ffb78666436 /kernel/srcu.c | |
parent | 486c8aba39e5f194519cd5c0e85e5d1de8b74b03 (diff) | |
parent | 66f75a5d028beaf67c931435fdc3e7823125730c (diff) | |
download | linux-57b8628bb0ac4e47c806e45c5bbd89282e93869b.tar.xz |
Merge commit 'v3.4-rc4' into next
Diffstat (limited to 'kernel/srcu.c')
-rw-r--r-- | kernel/srcu.c | 33 |
1 files changed, 23 insertions, 10 deletions
diff --git a/kernel/srcu.c b/kernel/srcu.c index 0febf61..ba35f3a 100644 --- a/kernel/srcu.c +++ b/kernel/srcu.c @@ -172,6 +172,12 @@ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void)) { int idx; + rcu_lockdep_assert(!lock_is_held(&sp->dep_map) && + !lock_is_held(&rcu_bh_lock_map) && + !lock_is_held(&rcu_lock_map) && + !lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section"); + idx = sp->completed; mutex_lock(&sp->mutex); @@ -280,19 +286,26 @@ void synchronize_srcu(struct srcu_struct *sp) EXPORT_SYMBOL_GPL(synchronize_srcu); /** - * synchronize_srcu_expedited - like synchronize_srcu, but less patient + * synchronize_srcu_expedited - Brute-force SRCU grace period * @sp: srcu_struct with which to synchronize. * - * Flip the completed counter, and wait for the old count to drain to zero. - * As with classic RCU, the updater must use some separate means of - * synchronizing concurrent updates. Can block; must be called from - * process context. + * Wait for an SRCU grace period to elapse, but use a "big hammer" + * approach to force the grace period to end quickly. This consumes + * significant time on all CPUs and is unfriendly to real-time workloads, + * so is thus not recommended for any sort of common-case code. In fact, + * if you are using synchronize_srcu_expedited() in a loop, please + * restructure your code to batch your updates, and then use a single + * synchronize_srcu() instead. * - * Note that it is illegal to call synchronize_srcu_expedited() - * from the corresponding SRCU read-side critical section; doing so - * will result in deadlock. However, it is perfectly legal to call - * synchronize_srcu_expedited() on one srcu_struct from some other - * srcu_struct's read-side critical section. + * Note that it is illegal to call this function while holding any lock + * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal + * to call this function from a CPU-hotplug notifier. Failing to observe + * these restriction will result in deadlock. It is also illegal to call + * synchronize_srcu_expedited() from the corresponding SRCU read-side + * critical section; doing so will result in deadlock. However, it is + * perfectly legal to call synchronize_srcu_expedited() on one srcu_struct + * from some other srcu_struct's read-side critical section, as long as + * the resulting graph of srcu_structs is acyclic. */ void synchronize_srcu_expedited(struct srcu_struct *sp) { |