From ae15018456c44b742d352af323e0b89eae4a6383 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 23 Apr 2013 13:20:57 -0700 Subject: [PATCH] rcu: Make call_rcu() leak callbacks for debug-object errors If someone does a duplicate call_rcu(), the worst thing the second call_rcu() could do would be to actually queue the callback the second time because doing so corrupts whatever list the callback was already queued on. This commit therefore makes __call_rcu() check the new return value from debug-objects and leak the callback upon error. This commit also substitutes rcu_leak_callback() for whatever callback function was previously in place in order to avoid freeing the callback out from under any readers that might still be referencing it. These changes increase the probability that the debug-objects error messages will actually make it somewhere visible. Signed-off-by: Paul E. McKenney Cc: Mathieu Desnoyers Cc: Sedat Dilek Cc: Davidlohr Bueso Cc: Rik van Riel Cc: Thomas Gleixner Cc: Linus Torvalds Tested-by: Sedat Dilek Reviewed-by: Josh Triplett --- kernel/rcu.h | 10 +++++++--- kernel/rcutree.c | 14 +++++++++++++- 2 files changed, 20 insertions(+), 4 deletions(-) diff --git a/kernel/rcu.h b/kernel/rcu.h index 0a90ccc65bfb..77131966c4ad 100644 --- a/kernel/rcu.h +++ b/kernel/rcu.h @@ -67,12 +67,15 @@ extern struct debug_obj_descr rcuhead_debug_descr; -static inline void debug_rcu_head_queue(struct rcu_head *head) +static inline int debug_rcu_head_queue(struct rcu_head *head) { - debug_object_activate(head, &rcuhead_debug_descr); + int r1; + + r1 = debug_object_activate(head, &rcuhead_debug_descr); debug_object_active_state(head, &rcuhead_debug_descr, STATE_RCU_HEAD_READY, STATE_RCU_HEAD_QUEUED); + return r1; } static inline void debug_rcu_head_unqueue(struct rcu_head *head) @@ -83,8 +86,9 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head) debug_object_deactivate(head, &rcuhead_debug_descr); } #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ -static inline void debug_rcu_head_queue(struct rcu_head *head) +static inline int debug_rcu_head_queue(struct rcu_head *head) { + return 0; } static inline void debug_rcu_head_unqueue(struct rcu_head *head) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index a7bf517b0482..91840566e294 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2304,6 +2304,13 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp, } } +/* + * RCU callback function to leak a callback. + */ +static void rcu_leak_callback(struct rcu_head *rhp) +{ +} + /* * Helper function for call_rcu() and friends. The cpu argument will * normally be -1, indicating "currently running CPU". It may specify @@ -2318,7 +2325,12 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), struct rcu_data *rdp; WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */ - debug_rcu_head_queue(head); + if (debug_rcu_head_queue(head)) { + /* Probable double call_rcu(), so leak the callback. */ + ACCESS_ONCE(head->func) = rcu_leak_callback; + WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n"); + return; + } head->func = func; head->next = NULL; -- 2.20.1