The following commit has been merged into the perf/urgent branch of tip:

Commit-ID: 003461559ef7a9bd0239bae35a22ad8924d6e9ad Gitweb: https://git.kernel.org/tip/003461559ef7a9bd0239bae35a22ad8924d6e9ad Author: Song Liu songliubraving@fb.com AuthorDate: Thu, 23 Jan 2020 10:11:46 -08:00 Committer: Ingo Molnar mingo@kernel.org CommitterDate: Tue, 28 Jan 2020 21:20:18 +01:00

perf/core: Fix mlock accounting in perf_mmap()

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 --- kernel/events/core.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c index 2173c23..2d9aeba 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5916,7 +5916,15 @@ 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) { /*