From 457139f16ae15d86df1e491fc45a9ea56def57b5 Mon Sep 17 00:00:00 2001 From: Zheng Yejian Date: Sat, 15 May 2021 22:06:30 +0800 Subject: acct: fix accuracy loss for input value of encode_comp_t() Patch series "Fix encode_comp_t()". Type conversion in encode_comp_t() may look a bit problematic. This patch (of 2): See calculation of ac_{u,s}time in fill_ac(): > ac->ac_utime = encode_comp_t(nsec_to_AHZ(pacct->ac_utime)); > ac->ac_stime = encode_comp_t(nsec_to_AHZ(pacct->ac_stime)); Return value of nsec_to_AHZ() is always type of 'u64', but it is handled as type of 'unsigned long' in encode_comp_t, and accuracy loss would happen on 32-bit platform when 'unsigned long' value is 32-bit-width. So 'u64' value of encode_comp_t() may look better. Link: https://lkml.kernel.org/r/20210515140631.369106-1-zhengyejian1@huawei.com Link: https://lkml.kernel.org/r/20210515140631.369106-2-zhengyejian1@huawei.com Signed-off-by: Zheng Yejian Cc: Hanjun Guo Cc: Randy Dunlap # build-tested Cc: Vlastimil Babka Cc: Zhang Jinhao Signed-off-by: Andrew Morton --- kernel/acct.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/acct.c b/kernel/acct.c index 62200d799b9b..31b09cf7189c 100644 --- a/kernel/acct.c +++ b/kernel/acct.c @@ -320,7 +320,7 @@ void acct_exit_ns(struct pid_namespace *ns) } /* - * encode an unsigned long into a comp_t + * encode an u64 into a comp_t * * This routine has been adopted from the encode_comp_t() function in * the kern_acct.c file of the FreeBSD operating system. The encoding @@ -331,7 +331,7 @@ void acct_exit_ns(struct pid_namespace *ns) #define EXPSIZE 3 /* Base 8 (3 bit) exponent. */ #define MAXFRACT ((1 << MANTSIZE) - 1) /* Maximum fractional value. */ -static comp_t encode_comp_t(unsigned long value) +static comp_t encode_comp_t(u64 value) { int exp, rnd; -- cgit v1.2.1