On Thu, Sep 04, 2014 at 09:43:11AM -0700, Peter Feiner wrote:
> On Mon, Aug 25, 2014 at 09:45:34PM -0700, Hugh Dickins wrote:
> > That sets me wondering: have you placed the VM_SOFTDIRTY check in the
> > right place in this series of tests?
> >
> > I think, once pgprot_modify() is correct on all
On Thu, Sep 04, 2014 at 09:43:11AM -0700, Peter Feiner wrote:
On Mon, Aug 25, 2014 at 09:45:34PM -0700, Hugh Dickins wrote:
That sets me wondering: have you placed the VM_SOFTDIRTY check in the
right place in this series of tests?
I think, once pgprot_modify() is correct on all
On Mon, Aug 25, 2014 at 09:45:34PM -0700, Hugh Dickins wrote:
> On Sun, 24 Aug 2014, Peter Feiner wrote:
> > With this patch, write notifications are enabled when VM_SOFTDIRTY is
> > cleared. Furthermore, to avoid unnecessary faults, write
> > notifications are disabled when VM_SOFTDIRTY is reset.
On Mon, Aug 25, 2014 at 09:45:34PM -0700, Hugh Dickins wrote:
On Sun, 24 Aug 2014, Peter Feiner wrote:
With this patch, write notifications are enabled when VM_SOFTDIRTY is
cleared. Furthermore, to avoid unnecessary faults, write
notifications are disabled when VM_SOFTDIRTY is reset.
On Wed, Aug 27, 2014 at 04:12:43PM -0700, Hugh Dickins wrote:
> > >
> > > Weak argument to me.
>
> Yes. However rarely it's modified, we don't want any chance of it
> corrupting another flag.
>
> VM_SOFTDIRTY is special in the sense that it's maintained in a very
> different way from the other
On Wed, Aug 27, 2014 at 04:12:43PM -0700, Hugh Dickins wrote:
Weak argument to me.
Yes. However rarely it's modified, we don't want any chance of it
corrupting another flag.
VM_SOFTDIRTY is special in the sense that it's maintained in a very
different way from the other VM_flags.
On Tue, 26 Aug 2014, Cyrill Gorcunov wrote:
> On Tue, Aug 26, 2014 at 06:43:55PM +0300, Kirill A. Shutemov wrote:
> > On Tue, Aug 26, 2014 at 07:18:13PM +0400, Cyrill Gorcunov wrote:
> > > > Basically, it's safe if only soft-dirty is allowed to modify vm_flags
> > > > without down_write(). But why
On Tue, 26 Aug 2014, Cyrill Gorcunov wrote:
> On Mon, Aug 25, 2014 at 09:45:34PM -0700, Hugh Dickins wrote:
> >
> > Hmm. For a long time I thought you were fixing another important bug
> > with down_write, since we "always" use down_write to modify vm_flags.
> >
> > But now I'm realizing that
On Tue, 26 Aug 2014, Cyrill Gorcunov wrote:
On Mon, Aug 25, 2014 at 09:45:34PM -0700, Hugh Dickins wrote:
Hmm. For a long time I thought you were fixing another important bug
with down_write, since we always use down_write to modify vm_flags.
But now I'm realizing that if this is the
On Tue, 26 Aug 2014, Cyrill Gorcunov wrote:
On Tue, Aug 26, 2014 at 06:43:55PM +0300, Kirill A. Shutemov wrote:
On Tue, Aug 26, 2014 at 07:18:13PM +0400, Cyrill Gorcunov wrote:
Basically, it's safe if only soft-dirty is allowed to modify vm_flags
without down_write(). But why is
On Tue, Aug 26, 2014 at 06:43:55PM +0300, Kirill A. Shutemov wrote:
> On Tue, Aug 26, 2014 at 07:18:13PM +0400, Cyrill Gorcunov wrote:
> > > Basically, it's safe if only soft-dirty is allowed to modify vm_flags
> > > without down_write(). But why is soft-dirty so special?
> >
> > because how we
On Tue, Aug 26, 2014 at 07:18:13PM +0400, Cyrill Gorcunov wrote:
> > Basically, it's safe if only soft-dirty is allowed to modify vm_flags
> > without down_write(). But why is soft-dirty so special?
>
> because how we use this bit, i mean in normal workload this bit won't
> be used intensively i
On Tue, Aug 26, 2014 at 05:56:12PM +0300, Kirill A. Shutemov wrote:
> > >
> > > It seems safe in vma-softdirty context. But if somebody else will decide
> > > that
> > > it's fine to modify vm_flags without down_write (in their context), we
> > > will get trouble. Sasha will come with weird bug
On Tue, Aug 26, 2014 at 06:19:14PM +0400, Cyrill Gorcunov wrote:
> On Tue, Aug 26, 2014 at 05:04:19PM +0300, Kirill A. Shutemov wrote:
> > > >
> > > > But now I'm realizing that if this is the _only_ place which modifies
> > > > vm_flags with down_read, then it's "probably" safe. I've a vague
>
On Tue, Aug 26, 2014 at 05:04:19PM +0300, Kirill A. Shutemov wrote:
> > >
> > > But now I'm realizing that if this is the _only_ place which modifies
> > > vm_flags with down_read, then it's "probably" safe. I've a vague
> > > feeling that this was discussed before - is that so, Cyrill?
> >
> >
On Tue, Aug 26, 2014 at 10:49:52AM +0400, Cyrill Gorcunov wrote:
> On Mon, Aug 25, 2014 at 09:45:34PM -0700, Hugh Dickins wrote:
> > > +static int clear_refs(struct mm_struct *mm, enum clear_refs_types type,
> > > + int write)
> > > +{
> ...
> > > +
> > > + if (write)
> > > +
On Mon, Aug 25, 2014 at 09:45:34PM -0700, Hugh Dickins wrote:
> > +static int clear_refs(struct mm_struct *mm, enum clear_refs_types type,
> > + int write)
> > +{
...
> > +
> > + if (write)
> > + down_write(>mmap_sem);
> > + else
> > +
On Mon, Aug 25, 2014 at 09:45:34PM -0700, Hugh Dickins wrote:
+static int clear_refs(struct mm_struct *mm, enum clear_refs_types type,
+ int write)
+{
...
+
+ if (write)
+ down_write(mm-mmap_sem);
+ else
+ down_read(mm-mmap_sem);
+
+
On Tue, Aug 26, 2014 at 10:49:52AM +0400, Cyrill Gorcunov wrote:
On Mon, Aug 25, 2014 at 09:45:34PM -0700, Hugh Dickins wrote:
+static int clear_refs(struct mm_struct *mm, enum clear_refs_types type,
+ int write)
+{
...
+
+ if (write)
+
On Tue, Aug 26, 2014 at 05:04:19PM +0300, Kirill A. Shutemov wrote:
But now I'm realizing that if this is the _only_ place which modifies
vm_flags with down_read, then it's probably safe. I've a vague
feeling that this was discussed before - is that so, Cyrill?
Well, as far as I
On Tue, Aug 26, 2014 at 06:19:14PM +0400, Cyrill Gorcunov wrote:
On Tue, Aug 26, 2014 at 05:04:19PM +0300, Kirill A. Shutemov wrote:
But now I'm realizing that if this is the _only_ place which modifies
vm_flags with down_read, then it's probably safe. I've a vague
feeling that
On Tue, Aug 26, 2014 at 05:56:12PM +0300, Kirill A. Shutemov wrote:
It seems safe in vma-softdirty context. But if somebody else will decide
that
it's fine to modify vm_flags without down_write (in their context), we
will get trouble. Sasha will come with weird bug report one day
On Tue, Aug 26, 2014 at 07:18:13PM +0400, Cyrill Gorcunov wrote:
Basically, it's safe if only soft-dirty is allowed to modify vm_flags
without down_write(). But why is soft-dirty so special?
because how we use this bit, i mean in normal workload this bit won't
be used intensively i think
On Tue, Aug 26, 2014 at 06:43:55PM +0300, Kirill A. Shutemov wrote:
On Tue, Aug 26, 2014 at 07:18:13PM +0400, Cyrill Gorcunov wrote:
Basically, it's safe if only soft-dirty is allowed to modify vm_flags
without down_write(). But why is soft-dirty so special?
because how we use this
On Sun, 24 Aug 2014, Peter Feiner wrote:
> For VMAs that don't want write notifications, PTEs created for read
> faults have their write bit set. If the read fault happens after
> VM_SOFTDIRTY is cleared, then the PTE's softdirty bit will remain
> clear after subsequent writes.
Good catch.
On Sun, 24 Aug 2014, Peter Feiner wrote:
For VMAs that don't want write notifications, PTEs created for read
faults have their write bit set. If the read fault happens after
VM_SOFTDIRTY is cleared, then the PTE's softdirty bit will remain
clear after subsequent writes.
Good catch. Worrying
For VMAs that don't want write notifications, PTEs created for read
faults have their write bit set. If the read fault happens after
VM_SOFTDIRTY is cleared, then the PTE's softdirty bit will remain
clear after subsequent writes.
Here's a simple code snippet to demonstrate the bug:
char* m =
For VMAs that don't want write notifications, PTEs created for read
faults have their write bit set. If the read fault happens after
VM_SOFTDIRTY is cleared, then the PTE's softdirty bit will remain
clear after subsequent writes.
Here's a simple code snippet to demonstrate the bug:
char* m =
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