Messages in this thread Patch in this message | | | From | Song Liu <> | Subject | [PATCH v2] perf/core: fix mlock accounting in perf_mmap() | Date | Wed, 22 Jan 2020 11:04:47 -0800 |
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sysctl_perf_event_mlock and user->locked_vm can change value independently, so we can't guarantee:
user->locked_vm <= user_lock_limit
When user->locked_vm is larger than user_lock_limit, we cannot simply update extra and user_extra as:
extra = user_locked - user_lock_limit; user_extra -= extra;
Otherwise, user_extra will be negative. In extreme cases, this may lead to negative user->locked_vm (until this perf-mmap is closed), which break locked_vm badly.
Fix this by adjusting user_locked before calculating extra and user_extra.
Fixes: c4b75479741c ("perf/core: Make the mlock accounting simple again") Signed-off-by: Song Liu <songliubraving@fb.com> Suggested-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> --- kernel/events/core.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 2173c23c25b4..d25f2de45996 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5916,8 +5916,19 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) */ 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 and user->locked_vm can change value + * independently. so we can't guarantee: + * user->locked_vm <= user_lock_limit + * + * Adjust user_locked to be <= user_lock_limit so we can calcualte + * correct extra and user_extra. + */ + user_locked = min_t(unsigned long, user_locked, user_lock_limit); + + user_locked += user_extra; if (user_locked > user_lock_limit) { /* * charge locked_vm until it hits user_lock_limit; -- 2.17.1
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