Messages in this thread Patch in this message | | | From | Song Liu <> | Subject | [PATCH] perf/core: fix mlock accounting in perf_mmap() | Date | Fri, 17 Jan 2020 15:45:03 -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 with two separate conditions, which make sure user_extra is always positive.
Fixes: c4b75479741c ("perf/core: Make the mlock accounting simple again") Signed-off-by: Song Liu <songliubraving@fb.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 | 28 ++++++++++++++++++++++++---- 1 file changed, 24 insertions(+), 4 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index a1f8bde19b56..89acdd1574ef 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5920,11 +5920,31 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) if (user_locked > user_lock_limit) { /* - * charge locked_vm until it hits user_lock_limit; - * charge the rest from pinned_vm + * sysctl_perf_event_mlock and user->locked_vm can change + * value independently, so we can't guarantee: + * + * user->locked_vm <= user_lock_limit + * + * We need be careful to make sure user_extra >=0. + * + * Using "user_locked - user_extra" to avoid calling + * atomic_long_read() again. */ - extra = user_locked - user_lock_limit; - user_extra -= extra; + if (user_locked - user_extra >= user_lock_limit) { + /* + * already used all user_locked_limit, charge all + * to pinned_vm + */ + extra = user_extra; + user_extra = 0; + } else { + /* + * charge locked_vm until it hits user_lock_limit; + * charge the rest from pinned_vm + */ + extra = user_locked - user_lock_limit; + user_extra -= extra; + } } lock_limit = rlimit(RLIMIT_MEMLOCK); -- 2.17.1
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