Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH v3 tip/core/rcu 04/40] srcu: Check for tardy grace-period activity in cleanup_srcu_struct() | Date | Wed, 19 Apr 2017 09:58:01 -0700 |
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Users of SRCU are obliged to complete all grace-period activity before invoking cleanup_srcu_struct(). This means that all calls to either synchronize_srcu() or synchronize_srcu_expedited() must have returned, and all calls to call_srcu() must have returned, and the last call to call_srcu() must have been followed by a call to srcu_barrier(). Furthermore, the caller must have done something to prevent any further calls to synchronize_srcu(), synchronize_srcu_expedited(), and call_srcu().
Therefore, if there has ever been an invocation of call_srcu() on the srcu_struct in question, the sequence of events must be as follows:
1. Prevent any further calls to call_srcu(). 2. Wait for any pre-existing call_srcu() invocations to return. 3. Invoke srcu_barrier(). 4. It is now safe to invoke cleanup_srcu_struct().
On the other hand, if there has ever been a call to synchronize_srcu() or synchronize_srcu_expedited(), the sequence of events must be as follows:
1. Prevent any further calls to synchronize_srcu() or synchronize_srcu_expedited(). 2. Wait for any pre-existing synchronize_srcu() or synchronize_srcu_expedited() invocations to return. 3. It is now safe to invoke cleanup_srcu_struct().
If there have been calls to all both types of functions (call_srcu() and either of synchronize_srcu() and synchronize_srcu_expedited()), then the caller must do the first three steps of the call_srcu() procedure above and the first two steps of the synchronize_s*() procedure above, and only then invoke cleanup_srcu_struct().
Note that cleanup_srcu_struct() does some probabilistic checks for the caller failing to follow these procedures, in which case cleanup_srcu_struct() does WARN_ON() and avoids freeing the per-CPU structures associated with the specified srcu_struct structure.
Reported-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> --- kernel/rcu/srcu.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c index ba41a5d04b49..e6da9fc1f0e9 100644 --- a/kernel/rcu/srcu.c +++ b/kernel/rcu/srcu.c @@ -254,13 +254,24 @@ static bool srcu_readers_active(struct srcu_struct *sp) * cleanup_srcu_struct - deconstruct a sleep-RCU structure * @sp: structure to clean up. * - * Must invoke this after you are finished using a given srcu_struct that - * was initialized via init_srcu_struct(), else you leak memory. + * Must invoke this only after you are finished using a given srcu_struct + * that was initialized via init_srcu_struct(). This code does some + * probabalistic checking, spotting late uses of srcu_read_lock(), + * synchronize_srcu(), synchronize_srcu_expedited(), and call_srcu(). + * If any such late uses are detected, the per-CPU memory associated with + * the srcu_struct is simply leaked and WARN_ON() is invoked. If the + * caller frees the srcu_struct itself, a use-after-free crash will likely + * ensue, but at least there will be a warning printed. */ void cleanup_srcu_struct(struct srcu_struct *sp) { if (WARN_ON(srcu_readers_active(sp))) return; /* Leakage unless caller handles error. */ + if (WARN_ON(!rcu_all_batches_empty(sp))) + return; /* Leakage unless caller handles error. */ + flush_delayed_work(&sp->work); + if (WARN_ON(sp->running)) + return; /* Caller forgot to stop doing call_srcu()? */ free_percpu(sp->per_cpu_ref); sp->per_cpu_ref = NULL; } -- 2.5.2
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