* [PATCH] timekeeping: improve arithmetic division in scale64_check_overflow()
@ 2020-01-20 10:05 Wen Yang
2020-03-04 9:20 ` [tip: timers/core] timekeeping: Prevent 32bit truncation " tip-bot2 for Wen Yang
0 siblings, 1 reply; 2+ messages in thread
From: Wen Yang @ 2020-01-20 10:05 UTC (permalink / raw)
To: John Stultz, Thomas Gleixner; +Cc: Wen Yang, Stephen Boyd, linux-kernel
do_div() does a 64-by-32 division. Use div64_u64() instead of it
if the divisor is u64, to avoid truncation to 32-bit.
And as a nice side effect also cleans up the function a bit.
Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: linux-kernel@vger.kernel.org
---
kernel/time/timekeeping.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index ca69290bee2a..4fc2af4367a7 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1005,9 +1005,8 @@ static int scale64_check_overflow(u64 mult, u64 div, u64 *base)
((int)sizeof(u64)*8 - fls64(mult) < fls64(rem)))
return -EOVERFLOW;
tmp *= mult;
- rem *= mult;
- do_div(rem, div);
+ rem = div64_u64(rem * mult, div);
*base = tmp + rem;
return 0;
}
--
2.23.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [tip: timers/core] timekeeping: Prevent 32bit truncation in scale64_check_overflow()
2020-01-20 10:05 [PATCH] timekeeping: improve arithmetic division in scale64_check_overflow() Wen Yang
@ 2020-03-04 9:20 ` tip-bot2 for Wen Yang
0 siblings, 0 replies; 2+ messages in thread
From: tip-bot2 for Wen Yang @ 2020-03-04 9:20 UTC (permalink / raw)
To: linux-tip-commits; +Cc: Wen Yang, Thomas Gleixner, x86, LKML
The following commit has been merged into the timers/core branch of tip:
Commit-ID: 4cbbc3a0eeed675449b1a4d080008927121f3da3
Gitweb: https://git.kernel.org/tip/4cbbc3a0eeed675449b1a4d080008927121f3da3
Author: Wen Yang <wenyang@linux.alibaba.com>
AuthorDate: Mon, 20 Jan 2020 18:05:23 +08:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 04 Mar 2020 10:17:51 +01:00
timekeeping: Prevent 32bit truncation in scale64_check_overflow()
While unlikely the divisor in scale64_check_overflow() could be >= 32bit in
scale64_check_overflow(). do_div() truncates the divisor to 32bit at least
on 32bit platforms.
Use div64_u64() instead to avoid the truncation to 32-bit.
[ tglx: Massaged changelog ]
Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200120100523.45656-1-wenyang@linux.alibaba.com
---
kernel/time/timekeeping.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index ca69290..4fc2af4 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1005,9 +1005,8 @@ static int scale64_check_overflow(u64 mult, u64 div, u64 *base)
((int)sizeof(u64)*8 - fls64(mult) < fls64(rem)))
return -EOVERFLOW;
tmp *= mult;
- rem *= mult;
- do_div(rem, div);
+ rem = div64_u64(rem * mult, div);
*base = tmp + rem;
return 0;
}
^ permalink raw reply related [flat|nested] 2+ messages in thread
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