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authorZheng Yejian <zhengyejian1@huawei.com>2021-05-15 22:06:30 +0800
committerAndrew Morton <akpm@linux-foundation.org>2022-11-30 16:13:18 -0800
commit457139f16ae15d86df1e491fc45a9ea56def57b5 (patch)
treeee2b4f536355921a5a6dfbcdab9029e6ea6bfa69
parentde985c109096b236d43e98da0c65376bf3bc24fb (diff)
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>
-rw-r--r--kernel/acct.c4
1 files 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;