On Wed, 2019-11-06 at 10:14 -0500, Josef Bacik wrote:
> On Wed, Nov 06, 2019 at 04:05:24PM +0100, Jan Kara wrote:
> > On Wed 06-11-19 09:56:09, Josef Bacik wrote:
> > I don't think this will work. AFAICS faultin_page() just checks
> > whether
> > 'nonblocking' is != NULL but doesn't ever look at its value...
> > Honestly the
> > whole interface is rather weird like lots of things around gup().
> >
>
> Oh what the hell, yeah this is super bonkers. The whole fault path
> probably
> should be cleaned up to handle retry better. This will do the trick
> I think?
I tried the patch, and it seems to fix the `mlockall(MCL_CURRENT)`
issue for "my test.c".
However, shutdown & reboot are still broken - i.e. the console says
"Reached target reboot" and "hangs forever". Shutdown & reboot work
with __get_user_pages_locked(). No clue what the difference there is.
Anyway, I've captured three smaps outputs: from 5.0.21, from
5.3.9+"nonblocking patch", from 5.3.9+"__get_user_pages_locked". All
three look okay to me - although I don't completely understand why some
areas are not locked (-> "Locked: 0kB") - but "Locked" is always equal
to "Pss", so I assume that's fine?
>
> Josef
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 8f236a335ae9..2468789298e6 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -628,7 +628,7 @@ static int faultin_page(struct task_struct *tsk,
> struct vm_area_struct *vma,
> fault_flags |= FAULT_FLAG_WRITE;
> if (*flags & FOLL_REMOTE)
> fault_flags |= FAULT_FLAG_REMOTE;
> - if (nonblocking)
> + if (nonblocking && *nonblocking != 0)
> fault_flags |= FAULT_FLAG_ALLOW_RETRY;
> if (*flags & FOLL_NOWAIT)
> fault_flags |= FAULT_FLAG_ALLOW_RETRY |
> FAULT_FLAG_RETRY_NOWAIT;
> @@ -1237,6 +1237,7 @@ int __mm_populate(unsigned long start, unsigned
> long len, int ignore_errors)
> unsigned long end, nstart, nend;
> struct vm_area_struct *vma = NULL;
> int locked = 0;
> + int nonblocking = 1;
> long ret = 0;
>
> end = start + len;
> @@ -1268,7 +1269,7 @@ int __mm_populate(unsigned long start, unsigned
> long len, int ignore_errors)
> * double checks the vma flags, so that it won't mlock
> pages
> * if the vma was already munlocked.
> */
> - ret = populate_vma_page_range(vma, nstart, nend,
> &locked);
> + ret = populate_vma_page_range(vma, nstart, nend,
> &nonblocking);
> if (ret < 0) {
> if (ignore_errors) {
> ret = 0;
> @@ -1276,6 +1277,14 @@ int __mm_populate(unsigned long start,
> unsigned long len, int ignore_errors)
> }
> break;
> }
> +
> + /*
> + * We dropped the mmap_sem, so we need to re-lock, and
> the next
> + * loop around we won't drop because nonblocking is now
> 0.
> + */
> + if (!nonblocking)
> + locked = 0;
> +
> nend = nstart + ret * PAGE_SIZE;
> ret = 0;
> }
Attachment:
smaps-5.0.21.txt.gz
Description: application/gzip
Attachment:
smaps-add-nonblocking.txt.gz
Description: application/gzip
Attachment:
smaps-get_user_pages_locked.txt.gz
Description: application/gzip
