From: Zheng Yejian <zhengyejian1@huawei.com>
To: <linux-kernel@vger.kernel.org>
Cc: <akpm@linux-foundation.org>, <rdunlap@infradead.org>,
<vbabka@suse.cz>, <guohanjun@huawei.com>,
<zhangjinhao2@huawei.com>
Subject: [PATCH 1/2] acct: Fix accuracy loss for input value of encode_comp_t()
Date: Sat, 15 May 2021 22:06:30 +0800 [thread overview]
Message-ID: <20210515140631.369106-2-zhengyejian1@huawei.com> (raw)
In-Reply-To: <20210515140631.369106-1-zhengyejian1@huawei.com>
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.
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
kernel/acct.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/acct.c b/kernel/acct.c
index a64102be2bb0..9e143ed5b5d0 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -301,7 +301,7 @@ 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
@@ -312,7 +312,7 @@ 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;
--
2.17.1
next prev parent reply other threads:[~2021-05-15 13:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-15 14:06 [PATCH 0/2] Fix encode_comp_t() Zheng Yejian
2021-05-15 14:06 ` Zheng Yejian [this message]
2021-05-15 14:06 ` [PATCH 2/2] acct: Fix potential integer overflow in encode_comp_t() Zheng Yejian
2022-11-02 3:52 ` [PATCH 0/2] Fix encode_comp_t() Zheng Yejian
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