diff options
| author | Zheng Zucheng <zhengzucheng@huawei.com> | 2024-07-26 02:32:35 +0000 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2024-07-29 12:22:32 +0200 |
| commit | 77baa5bafcbe1b2a15ef9c37232c21279c95481c (patch) | |
| tree | 5cd4305e5b58429c6de224a4d01df3c65e3c23a3 /kernel | |
| parent | 8400291e289ee6b2bf9779ff1c83a291501f017b (diff) | |
| download | linux-stable-77baa5bafcbe1b2a15ef9c37232c21279c95481c.tar.gz linux-stable-77baa5bafcbe1b2a15ef9c37232c21279c95481c.tar.bz2 linux-stable-77baa5bafcbe1b2a15ef9c37232c21279c95481c.zip | |
sched/cputime: Fix mul_u64_u64_div_u64() precision for cputime
In extreme test scenarios:
the 14th field utime in /proc/xx/stat is greater than sum_exec_runtime,
utime = 18446744073709518790 ns, rtime = 135989749728000 ns
In cputime_adjust() process, stime is greater than rtime due to
mul_u64_u64_div_u64() precision problem.
before call mul_u64_u64_div_u64(),
stime = 175136586720000, rtime = 135989749728000, utime = 1416780000.
after call mul_u64_u64_div_u64(),
stime = 135989949653530
unsigned reversion occurs because rtime is less than stime.
utime = rtime - stime = 135989749728000 - 135989949653530
= -199925530
= (u64)18446744073709518790
Trigger condition:
1). User task run in kernel mode most of time
2). ARM64 architecture
3). TICK_CPU_ACCOUNTING=y
CONFIG_VIRT_CPU_ACCOUNTING_NATIVE is not set
Fix mul_u64_u64_div_u64() conversion precision by reset stime to rtime
Fixes: 3dc167ba5729 ("sched/cputime: Improve cputime_adjust()")
Signed-off-by: Zheng Zucheng <zhengzucheng@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20240726023235.217771-1-zhengzucheng@huawei.com
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/cputime.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index a5e00293ae43..0bed0fa1acd9 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -582,6 +582,12 @@ void cputime_adjust(struct task_cputime *curr, struct prev_cputime *prev, } stime = mul_u64_u64_div_u64(stime, rtime, stime + utime); + /* + * Because mul_u64_u64_div_u64() can approximate on some + * achitectures; enforce the constraint that: a*b/(b+c) <= a. + */ + if (unlikely(stime > rtime)) + stime = rtime; update: /* |