Re: [PATCH mm-unstable] mm/madvise: handle MADV_{HWPOISON,SOFT_OFFLINE} from madvise_unlock()

[SeongJae Park <sj@kernel.org>]

On Tue, 11 Feb 2025 10:51:41 +0000 Lorenzo Stoakes <lorenzo.stoakes@oracle.com> wrote:

> +cc Naresh, Arnd for another reports/discussion of the same issue [0] while
> lore/lei is broken.
> 
> Hi,
> 
> Lore breaking means I missed this :) thankfully you cc'd me (_this_ is why I am
> so adament about people following get_maintainer.pl procedure btw) so I was able
> to now notice + reply :)
> 
> This is totally my bad for missing this on review, so mea culpa.

No worry, your reviews are always very helpful!

> 
> [0]:https://lwn.net/ml/linux-mm/CA+G9fYt5QwJ4_F8fJj7jx9_0Le9kOVSeG38ox9qnKqwsrDdvHQ@mail.gmail.com/
> 
> On Mon, Feb 10, 2025 at 10:32:01PM -0800, SeongJae Park wrote:
> > madvise_lock() does nothing for MADV_HWPOSION and MADV_SOFT_OFFLINE
> > behavior, but madvise_unlock() does mmap_lock unlocking regardless of
> > the behavior.
[...]
> >  mm/madvise.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index b5ef8e03d8b0..b8969457f3ef 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -1577,7 +1577,6 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
> >
> >  static int madvise_lock(struct mm_struct *mm, int behavior)
> >  {
> > -
> >  #ifdef CONFIG_MEMORY_FAILURE
> >  	if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
> >  		return 0;
> > @@ -1595,6 +1594,11 @@ static int madvise_lock(struct mm_struct *mm, int behavior)
> >
> >  static void madvise_unlock(struct mm_struct *mm, int behavior)
> >  {
> > +#ifdef CONFIG_MEMORY_FAILURE
> > +	if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
> > +		return;
> > +#endif
> 
> I agree this fixes the issue but this is horrible. let's abstract this please
> rather than doing the same crap that already existed, only now twice.

I agree abstracting this is a better idea.

> 
> > +
> >  	if (madvise_need_mmap_write(behavior))
> >  		mmap_write_unlock(mm);
> >  	else
> >
> > base-commit: 8bf30f9d23eb5040d37e6e712789cee8e71e1577
> > --
> > 2.39.5
> 
> I attach a fix-patch concept for something I think that'd be nicer, do with
> it what thy wilt! :P sorry I don't mean to be 'one of those' maintainers
> who copy/pastes code + demands somebody do it (by no means do I do so), but
> since this is so small I feel it's kind of quicker for me to do it this
> way.
> 
> Obviously take it or leave it/adapt it/etc. This is compile-tested only...

I further ran the repro program and confirmed this fixes the issue :)

> 
> ----8<----
> From 9fce3e47bf0fff2a2291be66002af346cdbca665 Mon Sep 17 00:00:00 2001
> From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Date: Tue, 11 Feb 2025 10:44:26 +0000
> Subject: [PATCH] mm/madvise: fix madvise_[un]lock() issue
> 
> We are asymmetric in our locking/unlocking in the case of memory failure
> madvise() behaviour options, correct this and abstract the memory failure
> check.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Reviewed-by: SeongJae Park <sj@kernel.org>
Tested-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

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