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rcu: Warn on for_each_leaf_node_cpu_mask() from non-leaf 

The for_each_leaf_node_cpu_mask() and for_each_leaf_node_possible_cpu()
macros must be invoked only on leaf rcu_node structures.  Failing to
abide by this restriction can result in infinite loops on systems with
more than 64 CPUs (or for more than 32 CPUs on 32-bit systems).  This
commit therefore adds WARN_ON_ONCE() calls to make misuse of these two
macros easier to debug.

Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2019-12-15 11:38:57 -08:00
parent 9f01eb5d49
commit 82dd8419e2
1 changed files with 4 additions and 2 deletions
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6
kernel/rcu/rcu.h
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@ -325,7 +325,8 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt)
* Iterate over all possible CPUs in a leaf RCU node.
*/
#define for_each_leaf_node_possible_cpu(rnp, cpu) \
for ((cpu) = cpumask_next((rnp)->grplo - 1, cpu_possible_mask); \
for (WARN_ON_ONCE(!rcu_is_leaf_node(rnp)), \
(cpu) = cpumask_next((rnp)->grplo - 1, cpu_possible_mask); \
(cpu) <= rnp->grphi; \
(cpu) = cpumask_next((cpu), cpu_possible_mask))
@ -335,7 +336,8 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt)
#define rcu_find_next_bit(rnp, cpu, mask) \
((rnp)->grplo + find_next_bit(&(mask), BITS_PER_LONG, (cpu)))
#define for_each_leaf_node_cpu_mask(rnp, cpu, mask) \
for ((cpu) = rcu_find_next_bit((rnp), 0, (mask)); \
for (WARN_ON_ONCE(!rcu_is_leaf_node(rnp)), \
(cpu) = rcu_find_next_bit((rnp), 0, (mask)); \
(cpu) <= rnp->grphi; \
(cpu) = rcu_find_next_bit((rnp), (cpu) + 1 - (rnp->grplo), (mask)))