Cc: Alexander Viro <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Peter Zijlstra (Intel) <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Vineet Gupta <[email protected]>
---
fs/exec.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 1977c2a553ac..25078627f048 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1690,15 +1690,10 @@ EXPORT_SYMBOL(set_binfmt);
*/
void set_dumpable(struct mm_struct *mm, int value)
{
- unsigned long old, new;
-
if (WARN_ON((unsigned)value > SUID_DUMP_ROOT))
return;
- do {
- old = ACCESS_ONCE(mm->flags);
- new = (old & ~MMF_DUMPABLE_MASK) | value;
- } while (cmpxchg(&mm->flags, old, new) != old);
+ set_mask_bits(&mm->flags, MMF_DUMPABLE_MASK, value);
}
SYSCALL_DEFINE3(execve,
--
1.9.1
On 08/07, Vineet Gupta wrote:
>
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1690,15 +1690,10 @@ EXPORT_SYMBOL(set_binfmt);
> */
> void set_dumpable(struct mm_struct *mm, int value)
> {
> - unsigned long old, new;
> -
> if (WARN_ON((unsigned)value > SUID_DUMP_ROOT))
> return;
>
> - do {
> - old = ACCESS_ONCE(mm->flags);
> - new = (old & ~MMF_DUMPABLE_MASK) | value;
> - } while (cmpxchg(&mm->flags, old, new) != old);
> + set_mask_bits(&mm->flags, MMF_DUMPABLE_MASK, value);
> }
Acked-by: Oleg Nesterov <[email protected]>
On Friday 07 August 2015 05:27 PM, Oleg Nesterov wrote:
> On 08/07, Vineet Gupta wrote:
>>
>> --- a/fs/exec.c
>> +++ b/fs/exec.c
>> @@ -1690,15 +1690,10 @@ EXPORT_SYMBOL(set_binfmt);
>> */
>> void set_dumpable(struct mm_struct *mm, int value)
>> {
>> - unsigned long old, new;
>> -
>> if (WARN_ON((unsigned)value > SUID_DUMP_ROOT))
>> return;
>>
>> - do {
>> - old = ACCESS_ONCE(mm->flags);
>> - new = (old & ~MMF_DUMPABLE_MASK) | value;
>> - } while (cmpxchg(&mm->flags, old, new) != old);
>> + set_mask_bits(&mm->flags, MMF_DUMPABLE_MASK, value);
>> }
>
> Acked-by: Oleg Nesterov <[email protected]>
I have a fundamental question though, perhaps stupid, do use cases like these
warrant the data to be atomic_t in first place. Do API like set_mask_bits() make
sense at all - or shd they be moved to atomic_* (after changing the underlying data)
See, I have such a cmpxchg loop in ARC code - originally from Peter :-)
arch/arc/kernel/smp.c. @ipi_data_ptr is NOT atomic_t
do {
new = old = ACCESS_ONCE(*ipi_data_ptr);
new |= 1U << msg;
} while (cmpxchg(ipi_data_ptr, old, new) != old);
Given that ARC (and some other RISC cores) lack native cmpxchg, we use LLSC
instructions to implement atomics including cpmxchg - the implementation itself
ensures loop is builtin making the outer loping superfluous and waste of cycles
(see e.g. cover letter @ http://www.spinics.net/lists/kernel/msg2029217.html)
So I wanted to convert that loop (and similar other cases to "some" API which
could be built conditionally based on cmpxchg or llsc. None such exist and I was
thinking of converting my case to atomic_t. Is that the right approach ?
Thx,
-Vineet
On Fri, Aug 07, 2015 at 08:14:03PM +0530, Vineet Gupta wrote:
> See, I have such a cmpxchg loop in ARC code - originally from Peter :-)
> arch/arc/kernel/smp.c. @ipi_data_ptr is NOT atomic_t
>
> do {
> new = old = ACCESS_ONCE(*ipi_data_ptr);
> new |= 1U << msg;
> } while (cmpxchg(ipi_data_ptr, old, new) != old);
>
Well, you'll have atomic_or() real soon now.
On Friday 07 August 2015 08:27 PM, Peter Zijlstra wrote:
> On Fri, Aug 07, 2015 at 08:14:03PM +0530, Vineet Gupta wrote:
>
>> > See, I have such a cmpxchg loop in ARC code - originally from Peter :-)
>> > arch/arc/kernel/smp.c. @ipi_data_ptr is NOT atomic_t
>> >
>> > do {
>> > new = old = ACCESS_ONCE(*ipi_data_ptr);
>> > new |= 1U << msg;
>> > } while (cmpxchg(ipi_data_ptr, old, new) != old);
>> >
> Well, you'll have atomic_or() real soon now.
Doesn't help my cause - ipi_data_ptr is not atomic_t - hence my prev question in
this thread
On Fri, Aug 07, 2015 at 09:05:06PM +0530, Vineet Gupta wrote:
> On Friday 07 August 2015 08:27 PM, Peter Zijlstra wrote:
> > On Fri, Aug 07, 2015 at 08:14:03PM +0530, Vineet Gupta wrote:
> >
> >> > See, I have such a cmpxchg loop in ARC code - originally from Peter :-)
> >> > arch/arc/kernel/smp.c. @ipi_data_ptr is NOT atomic_t
> >> >
> >> > do {
> >> > new = old = ACCESS_ONCE(*ipi_data_ptr);
> >> > new |= 1U << msg;
> >> > } while (cmpxchg(ipi_data_ptr, old, new) != old);
> >> >
> > Well, you'll have atomic_or() real soon now.
>
> Doesn't help my cause - ipi_data_ptr is not atomic_t - hence my prev question in
> this thread
A cast will work :-)
But yes, ideally everything will be type safe because of those archs
that cannot have atomic RmW ops like !ARC_HAS_LLSC.
Mixing cmpxchg()/xchg() with regular stores is broken on those.
Fwiw, you might want to set ARCH_SUPPORTS_ATOMIC_RMW for ARC_HAS_LLSC.
On Friday 07 August 2015 09:15 PM, Peter Zijlstra wrote:
> On Fri, Aug 07, 2015 at 09:05:06PM +0530, Vineet Gupta wrote:
>> On Friday 07 August 2015 08:27 PM, Peter Zijlstra wrote:
>>> On Fri, Aug 07, 2015 at 08:14:03PM +0530, Vineet Gupta wrote:
>>>
>>>>> See, I have such a cmpxchg loop in ARC code - originally from Peter :-)
>>>>> arch/arc/kernel/smp.c. @ipi_data_ptr is NOT atomic_t
>>>>>
>>>>> do {
>>>>> new = old = ACCESS_ONCE(*ipi_data_ptr);
>>>>> new |= 1U << msg;
>>>>> } while (cmpxchg(ipi_data_ptr, old, new) != old);
>>>>>
>>> Well, you'll have atomic_or() real soon now.
>>
>> Doesn't help my cause - ipi_data_ptr is not atomic_t - hence my prev question in
>> this thread
>
> A cast will work :-)
>
How ? We have
typedef struct {
int counter;
} atomic_t;
> But yes, ideally everything will be type safe because of those archs
> that cannot have atomic RmW ops like !ARC_HAS_LLSC.
Type safe - how / what ?
>
> Mixing cmpxchg()/xchg() with regular stores is broken on those.
Right, but how does that relate to this discussion - perhaps I shd stop talking -
long friday already :-)
>
> Fwiw, you might want to set ARCH_SUPPORTS_ATOMIC_RMW for ARC_HAS_LLSC.
>
Sure I will !
On Fri, Aug 07, 2015 at 09:28:05PM +0530, Vineet Gupta wrote:
> On Friday 07 August 2015 09:15 PM, Peter Zijlstra wrote:
> > On Fri, Aug 07, 2015 at 09:05:06PM +0530, Vineet Gupta wrote:
> >> On Friday 07 August 2015 08:27 PM, Peter Zijlstra wrote:
> >>> On Fri, Aug 07, 2015 at 08:14:03PM +0530, Vineet Gupta wrote:
> >>>
> >>>>> See, I have such a cmpxchg loop in ARC code - originally from Peter :-)
> >>>>> arch/arc/kernel/smp.c. @ipi_data_ptr is NOT atomic_t
> >>>>>
> >>>>> do {
> >>>>> new = old = ACCESS_ONCE(*ipi_data_ptr);
> >>>>> new |= 1U << msg;
> >>>>> } while (cmpxchg(ipi_data_ptr, old, new) != old);
> >>>>>
> >>> Well, you'll have atomic_or() real soon now.
> >>
> >> Doesn't help my cause - ipi_data_ptr is not atomic_t - hence my prev question in
> >> this thread
> >
> > A cast will work :-)
> >
>
> How ? We have
>
> typedef struct {
> int counter;
> } atomic_t;
ARC is 32bit, right? So int and unsigned long are of the same size.
Therefore:
atomic_or(1 << msg, (atomic_t *)ipi_data_ptr);
Ugly, yes, but it should DTRT.
> > But yes, ideally everything will be type safe because of those archs
> > that cannot have atomic RmW ops like !ARC_HAS_LLSC.
>
> Type safe - how / what ?
All atomic stuff restricted to atomic*t and bitmap functions (and
ideally we'd also have bitmap_t to avoid passing random unsigned long *
into bitmap functions and praying it all works, we do, and it doesn't,
well mostly :-).
> > Mixing cmpxchg()/xchg() with regular stores is broken on those.
>
> Right, but how does that relate to this discussion - perhaps I shd stop talking -
> long friday already :-)
:-)
Well, its a very good argument for why we should not use cmpxchg/xchg on
!atomic*t types, and therefore why the function at hand (set_mask_bit)
should really be on an atomic_t.
That said, it will probably make the fs code fugly for having to use
atomic_t and all its accessors all over the place.