Messages in this thread | | | Date | Tue, 23 Jul 2019 16:11:09 +0800 | From | Yang Xu <> | Subject | Re: [PATCH] sys_prctl(): simplify arg2 judgment when calling PR_SET_TIMERSLACK |
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on 2019/07/23 15:23, Cyrill Gorcunov wrote:
> On Tue, Jul 23, 2019 at 11:30:53AM +0800, Yang Xu wrote: >> arg2 will never< 0, for its type is 'unsigned long'. So negative >> judgment is meaningless. >> >> Signed-off-by: Yang Xu<xuyang2018.jy@cn.fujitsu.com> >> --- >> kernel/sys.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/kernel/sys.c b/kernel/sys.c >> index 2969304c29fe..399457d26bef 100644 >> --- a/kernel/sys.c >> +++ b/kernel/sys.c >> @@ -2372,11 +2372,11 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, >> error = current->timer_slack_ns; >> break; >> case PR_SET_TIMERSLACK: >> - if (arg2<= 0) >> + if (arg2) >> + current->timer_slack_ns = arg2; >> + else >> current->timer_slack_ns = >> current->default_timer_slack_ns; >> - else >> - current->timer_slack_ns = arg2; >> break; >> case PR_MCE_KILL: >> if (arg4 | arg5) > > From a glance it looks correct to me, but then... > > 1) you might simply compare with zero, iow if (arg2 == 0) > instead of changing 7 lines Hi Cyril
Indeed. simply compare with zero might be better.
> 2) according to man page passing negative value should be acceptable, > though it never worked as expected. I've been grepping "git log" > for this file and the former API is coming from > > commit 6976675d94042fbd446231d1bd8b7de71a980ada > Author: Arjan van de Ven<arjan@linux.intel.com> > Date: Mon Sep 1 15:52:40 2008 -0700 > > hrtimer: create a "timer_slack" field in the task struct > > which is 11 years old by now. Nobody complained so far even when man > page is saying pretty obviously > > PR_SET_TIMERSLACK (since Linux 2.6.28) > Each thread has two associated timer slack values: a "default" > value, and a "current" value. This operation sets the "current" > timer slack value for the calling thread. If the nanosecond > value supplied in arg2 is greater than zero, then the "current" > value is set to this value. If arg2 is less than or equal to > zero, the "current" timer slack is reset to the thread's > "default" timer slack value. > > So i think to match the man page (and assuming that accepting negative value > has been supposed) we should rather do > > if ((long)arg2< 0) Looks correct. But if we set a ULONG_MAX(PR_GET_TIMERSLACK also limits ULONG_MAX) value(about 4s) on 32bit machine, this code will think this value is a negative value and use default value.
I guess man page was written as "less than or equal to zero" because of this confusing code(arg2<=0, but arg2 is an unsinged long value). I think we can change this man page and also add bounds value description.
Also, I found a patch about arg2 is an unsigned long value
commit 7fe5e04292e71af34ae171b88caa2a139e0b6125 Author: Chen Gang<gang.chen@asianux.com> Date: Thu Feb 21 16:43:06 2013 -0800
sys_prctl(): arg2 is unsigned long which is never< 0
arg2 will never< 0, for its type is 'unsigned long'
Also, use the provided macros.
What do you think about it ?
> Thoughts? > > >
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