From: "Paul E. McKenney" <[email protected]> In some cases, the allocator return address is in a common function, so that more information is desired. For example, percpu_ref reference-count underflow happens in an RCU callback function having access only to a block of memory that is always allocated in percpu_ref_init(). This information is unhelpful.
This commit therefore causes the percpu_ref_switch_to_atomic_rcu() function to use the new kmem_last_alloc_stack() function to collect and print a stack trace upon reference-count underflow. This requires the kernel use the slub allocator and be built with CONFIG_STACKTRACE=y. As always, slub debugging must be enabled one way or another, for example, by booting with the "slub_debug=U" kernel boot parameter. Cc: Ming Lei <[email protected]> Cc: Jens Axboe <[email protected]> Reported-by: Andrii Nakryiko <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> --- lib/percpu-refcount.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c index 8c7b21a0..ebdfa47 100644 --- a/lib/percpu-refcount.c +++ b/lib/percpu-refcount.c @@ -169,8 +169,6 @@ static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu) struct percpu_ref *ref = data->ref; unsigned long __percpu *percpu_count = percpu_count_ptr(ref); unsigned long count = 0; - void *allocaddr; - const char *allocerr; int cpu; for_each_possible_cpu(cpu) @@ -194,14 +192,26 @@ static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu) atomic_long_add((long)count - PERCPU_COUNT_BIAS, &data->count); if (atomic_long_read(&data->count) <= 0) { - allocaddr = kmem_last_alloc(data); + void *allocaddr; + const char *allocerr; + void *allocstack[8]; + int i; + + allocaddr = kmem_last_alloc_stack(data, allocstack, ARRAY_SIZE(allocstack)); allocerr = kmem_last_alloc_errstring(allocaddr); - if (allocerr) + if (allocerr) { WARN_ONCE(1, "percpu ref (%ps) <= 0 (%ld) after switching to atomic (%s)", data->release, atomic_long_read(&data->count), allocerr); - else - WARN_ONCE(1, "percpu ref (%ps) <= 0 (%ld) after switching to atomic (allocated at %pS)", - data->release, atomic_long_read(&data->count), allocaddr); + } else { + pr_err("percpu ref (%ps) <= 0 (%ld) after switching to atomic (allocated at %pS)\n", + data->release, atomic_long_read(&data->count), allocaddr); + for (i = 0; i < ARRAY_SIZE(allocstack); i++) { + if (!allocstack[i]) + break; + pr_err("\t%pS\n", allocstack[i]); + } + WARN_ON_ONCE(1); + } } /* @ref is viewed as dead on all CPUs, send out switch confirmation */ -- 2.9.5
