From: Song Liu songliubraving@fb.com
commit 003461559ef7a9bd0239bae35a22ad8924d6e9ad upstream.
Decreasing sysctl_perf_event_mlock between two consecutive perf_mmap()s of a perf ring buffer may lead to an integer underflow in locked memory accounting. This may lead to the undesired behaviors, such as failures in BPF map creation.
Address this by adjusting the accounting logic to take into account the possibility that the amount of already locked memory may exceed the current limit.
Fixes: c4b75479741c ("perf/core: Make the mlock accounting simple again") Suggested-by: Alexander Shishkin alexander.shishkin@linux.intel.com Signed-off-by: Song Liu songliubraving@fb.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Cc: stable@vger.kernel.org Acked-by: Alexander Shishkin alexander.shishkin@linux.intel.com Link: https://lkml.kernel.org/r/20200123181146.2238074-1-songliubraving@fb.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/events/core.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
--- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4887,7 +4887,15 @@ accounting: */ user_lock_limit *= num_online_cpus();
- user_locked = atomic_long_read(&user->locked_vm) + user_extra; + user_locked = atomic_long_read(&user->locked_vm); + + /* + * sysctl_perf_event_mlock may have changed, so that + * user->locked_vm > user_lock_limit + */ + if (user_locked > user_lock_limit) + user_locked = user_lock_limit; + user_locked += user_extra;
if (user_locked > user_lock_limit) extra = user_locked - user_lock_limit;