On Tue 29-09-20 11:00:03, Daniel Vetter wrote:
> On Tue, Sep 29, 2020 at 10:19:38AM +0200, Michal Hocko wrote:
> > On Wed 16-09-20 23:43:02, Daniel Vetter wrote:
> > > I can
> > > then figure out whether it's better to risk not spotting issues with
> > > call_rcu vs slapping a memalloc_noio_save/re
On Tue, Sep 29, 2020 at 10:19:38AM +0200, Michal Hocko wrote:
> On Wed 16-09-20 23:43:02, Daniel Vetter wrote:
> > I can
> > then figure out whether it's better to risk not spotting issues with
> > call_rcu vs slapping a memalloc_noio_save/restore around all these
> > critical section which force-d
On Wed 16-09-20 23:43:02, Daniel Vetter wrote:
> I can
> then figure out whether it's better to risk not spotting issues with
> call_rcu vs slapping a memalloc_noio_save/restore around all these
> critical section which force-degrades any allocation to GFP_ATOMIC at
did you mean memalloc_noreclaim
On Thu, Sep 17, 2020 at 09:52:30AM +0200, Daniel Vetter wrote:
> On Thu, Sep 17, 2020 at 12:39 AM Paul E. McKenney wrote:
> >
> > On Wed, Sep 16, 2020 at 11:43:02PM +0200, Daniel Vetter wrote:
> > > On Wed, Sep 16, 2020 at 10:58 PM Paul E. McKenney
> > > wrote:
> > > >
> > > > On Wed, Sep 16, 20
On Wed, 16 Sep 2020 at 21:32, Linus Torvalds
wrote:
>
> But something like a driver list walking thing should not be doing
> different things behind peoples back depending on whether they hold
> spinlocks or not. It should either just work regardless, or there
> should be a flag (or special interf
On Wed, Sep 16, 2020 at 11:43:02PM +0200, Daniel Vetter wrote:
> On Wed, Sep 16, 2020 at 10:58 PM Paul E. McKenney wrote:
> >
> > On Wed, Sep 16, 2020 at 10:29:06PM +0200, Daniel Vetter wrote:
> > > On Wed, Sep 16, 2020 at 5:29 PM Paul E. McKenney
> > > wrote:
> > > >
> > > > On Wed, Sep 16, 202
On Thu, Sep 17, 2020 at 12:39 AM Paul E. McKenney wrote:
>
> On Wed, Sep 16, 2020 at 11:43:02PM +0200, Daniel Vetter wrote:
> > On Wed, Sep 16, 2020 at 10:58 PM Paul E. McKenney
> > wrote:
> > >
> > > On Wed, Sep 16, 2020 at 10:29:06PM +0200, Daniel Vetter wrote:
> > > > On Wed, Sep 16, 2020 at
On Wed, Sep 16, 2020 at 10:58 PM Paul E. McKenney wrote:
>
> On Wed, Sep 16, 2020 at 10:29:06PM +0200, Daniel Vetter wrote:
> > On Wed, Sep 16, 2020 at 5:29 PM Paul E. McKenney wrote:
> > >
> > > On Wed, Sep 16, 2020 at 09:37:17AM +0200, Daniel Vetter wrote:
> > > > On Tue, Sep 15, 2020 at 7:35 P
On Wed, Sep 16, 2020 at 10:29:06PM +0200, Daniel Vetter wrote:
> On Wed, Sep 16, 2020 at 5:29 PM Paul E. McKenney wrote:
> >
> > On Wed, Sep 16, 2020 at 09:37:17AM +0200, Daniel Vetter wrote:
> > > On Tue, Sep 15, 2020 at 7:35 PM Linus Torvalds
> > > wrote:
> > > >
> > > > On Tue, Sep 15, 2020 at
On Wed, Sep 16, 2020 at 11:32:00AM -0700, Linus Torvalds wrote:
> On Wed, Sep 16, 2020 at 8:29 AM Paul E. McKenney wrote:
> >
> > All fair, but some of us need to write code that must handle being
> > invoked from a wide variety of contexts.
>
> Note that I think that core functionality is differ
On Wed, Sep 16, 2020 at 08:23:52PM +0100, Matthew Wilcox wrote:
> On Mon, Sep 14, 2020 at 11:55:24PM +0200, Thomas Gleixner wrote:
> > But just look at any check which uses preemptible(), especially those
> > which check !preemptible():
>
> hmm.
>
> +++ b/include/linux/preempt.h
> @@ -180,7 +180,
On Wed, Sep 16, 2020 at 09:37:17AM +0200, Daniel Vetter wrote:
> On Tue, Sep 15, 2020 at 7:35 PM Linus Torvalds
> wrote:
> >
> > On Tue, Sep 15, 2020 at 1:39 AM Thomas Gleixner wrote:
> > >
> > > OTOH, having a working 'preemptible()' or maybe better named
> > > 'can_schedule()' check makes tons
On Wed, Sep 16, 2020 at 5:29 PM Paul E. McKenney wrote:
>
> On Wed, Sep 16, 2020 at 09:37:17AM +0200, Daniel Vetter wrote:
> > On Tue, Sep 15, 2020 at 7:35 PM Linus Torvalds
> > wrote:
> > >
> > > On Tue, Sep 15, 2020 at 1:39 AM Thomas Gleixner
> > > wrote:
> > > >
> > > > OTOH, having a workin
On Mon, Sep 14, 2020 at 11:55:24PM +0200, Thomas Gleixner wrote:
> But just look at any check which uses preemptible(), especially those
> which check !preemptible():
hmm.
+++ b/include/linux/preempt.h
@@ -180,7 +180,9 @@ do { \
#define preempt_enable_no_resched() sched_preempt_enable_no_resch
On Tue, Sep 15, 2020 at 12:57 PM Thomas Gleixner wrote:
>
> You wish. I just found a 7 year old bug in a 10G network driver which
> surely would have been found if people would enable debug configs and
> not just run the crap on their PREEMPT_NONE, all debug off kernel. And
> that driver is not su
On Wed, Sep 16, 2020 at 8:29 AM Paul E. McKenney wrote:
>
> All fair, but some of us need to write code that must handle being
> invoked from a wide variety of contexts.
Note that I think that core functionality is different from random drivers.
Of course core code can (and will) look at things
On Tue, Sep 15, 2020 at 7:35 PM Linus Torvalds
wrote:
>
> On Tue, Sep 15, 2020 at 1:39 AM Thomas Gleixner wrote:
> >
> > OTOH, having a working 'preemptible()' or maybe better named
> > 'can_schedule()' check makes tons of sense to make decisions about
> > allocation modes or other things.
>
> No
On Tue, Sep 15 2020 at 10:35, Linus Torvalds wrote:
> On Tue, Sep 15, 2020 at 1:39 AM Thomas Gleixner wrote:
>>
>> OTOH, having a working 'preemptible()' or maybe better named
>> 'can_schedule()' check makes tons of sense to make decisions about
>> allocation modes or other things.
>
> No. I think
On Mon, Sep 14, 2020 at 01:59:15PM -0700, Linus Torvalds wrote:
> On Mon, Sep 14, 2020 at 1:45 PM Thomas Gleixner wrote:
> >
> > Recently merged code does:
> >
> > gfp = preemptible() ? GFP_KERNEL : GFP_ATOMIC;
> >
> > Looks obviously correct, except for the fact that preemptible() is
> >
On Tue, Sep 15, 2020 at 1:39 AM Thomas Gleixner wrote:
>
> OTOH, having a working 'preemptible()' or maybe better named
> 'can_schedule()' check makes tons of sense to make decisions about
> allocation modes or other things.
No. I think that those kinds of decisions about actual behavior are
alwa
On Tue, Sep 15, 2020 at 12:24 AM Thomas Gleixner wrote:
>
> Alternatively we just make highmem a bit more expensive by making these
> maps preemptible. RT is doing this for a long time and it's not that
> horrible.
Ack.
In fact, I've wanted to start just removing kmap support entirely. At
some p
On Tue, 15 Sep 2020 at 01:43, Linus Torvalds
wrote:
>
> On Mon, Sep 14, 2020 at 3:24 PM Linus Torvalds
> wrote:
> >
> > Ard and Herbert added to participants: see
> > chacha20poly1305_crypt_sg_inplace(), which does
> >
> > flags = SG_MITER_TO_SG;
> > if (!preemptible())
> >
On Mon, Sep 14 2020 at 15:24, Linus Torvalds wrote:
> On Mon, Sep 14, 2020 at 2:55 PM Thomas Gleixner wrote:
>>
>> Yes it does generate better code, but I tried hard to spot a difference
>> in various metrics exposed by perf. It's all in the noise and I only
>> can spot a difference when the actua
On Mon, Sep 14 2020 at 23:39, Linus Torvalds wrote:
> On Mon, Sep 14, 2020 at 11:24 PM Herbert Xu
> wrote:
>> > But another reason I tried to avoid kmap_atomic() is that it disables
>> > preemption unconditionally, even on 64-bit architectures where HIGHMEM
>> > is irrelevant. So using kmap_atomi
On Mon, Sep 14, 2020 at 11:24 PM Herbert Xu wrote:
>
> On Tue, Sep 15, 2020 at 09:20:59AM +0300, Ard Biesheuvel wrote:
> >
> > The documentation of kmap_atomic() states the following:
> >
> > * The use of kmap_atomic/kunmap_atomic is discouraged - kmap/kunmap
> > * gives a more generic (and cach
On Tue, Sep 15, 2020 at 09:20:59AM +0300, Ard Biesheuvel wrote:
>
> The documentation of kmap_atomic() states the following:
>
> * The use of kmap_atomic/kunmap_atomic is discouraged - kmap/kunmap
> * gives a more generic (and caching) interface. But kmap_atomic can
> * be used in IRQ contexts,
On Mon, Sep 14, 2020 at 3:24 PM Linus Torvalds
wrote:
>
> Ard and Herbert added to participants: see
> chacha20poly1305_crypt_sg_inplace(), which does
>
> flags = SG_MITER_TO_SG;
> if (!preemptible())
> flags |= SG_MITER_ATOMIC;
>
> introduced in commit d95312a3ccc0
On Mon, Sep 14, 2020 at 2:55 PM Thomas Gleixner wrote:
>
> Yes it does generate better code, but I tried hard to spot a difference
> in various metrics exposed by perf. It's all in the noise and I only
> can spot a difference when the actual preemption check after the
> decrement
I'm somewhat mor
On Mon, Sep 14 2020 at 13:59, Linus Torvalds wrote:
> On Mon, Sep 14, 2020 at 1:45 PM Thomas Gleixner wrote:
>>
>> Recently merged code does:
>>
>> gfp = preemptible() ? GFP_KERNEL : GFP_ATOMIC;
>>
>> Looks obviously correct, except for the fact that preemptible() is
>> unconditionally fa
On Mon, Sep 14, 2020 at 1:45 PM Thomas Gleixner wrote:
>
> Recently merged code does:
>
> gfp = preemptible() ? GFP_KERNEL : GFP_ATOMIC;
>
> Looks obviously correct, except for the fact that preemptible() is
> unconditionally false for CONFIF_PREEMPT_COUNT=n, i.e. all allocations in
> tha
Folks!
While working on various preempt count related things, I stumbled (again)
over the inconsistency of our preempt count handling.
The handling of preempt_count() is inconsistent accross kernel
configurations. On kernels which have PREEMPT_COUNT=n
preempt_disable/enable() and the lock/unlock
On Mon, 14 Sep 2020 22:42:09 +0200
Thomas Gleixner wrote:
> 21 files changed, 23 insertions(+), 92 deletions(-)
This alone makes it look promising, and hopefully acceptable by Linus :-)
-- Steve
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