From 026d9148a8aceea7d27d165446f8bd4fb95c6f40 Mon Sep 17 00:00:00 2001 From: Song Liu Date: Thu, 23 Jan 2020 10:11:46 -0800 Subject: [PATCH] perf/core: Fix mlock accounting in perf_mmap() 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 Signed-off-by: Song Liu Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Cc: Acked-by: Alexander Shishkin Link: https://lkml.kernel.org/r/20200123181146.2238074-1-songliubraving@fb.com Signed-off-by: Greg Kroah-Hartman --- 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 64ace5e9af2a..97b90faceb97 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5303,7 +5303,15 @@ 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;