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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 <zhengyejian1@huawei.com>
Cc: Hanjun Guo <guohanjun@huawei.com>
Cc: Randy Dunlap <rdunlap@infradead.org> # build-tested
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zhang Jinhao <zhangjinhao2@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Zheng Yejian 2021-05-15 22:06:30 +08:00 committed by Andrew Morton
parent de985c1090
commit 457139f16a
1 changed files with 2 additions and 2 deletions
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4
kernel/acct.c
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@ -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 * This routine has been adopted from the encode_comp_t() function in
* the kern_acct.c file of the FreeBSD operating system. The encoding * 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 EXPSIZE 3 /* Base 8 (3 bit) exponent. */
#define MAXFRACT ((1 << MANTSIZE) - 1) /* Maximum fractional value. */ #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; int exp, rnd;