The patch titled
Subject: mm/gup: remove the restriction on locked with FOLL_LONGTERM
has been added to the -mm mm-unstable branch. Its filename is
mm-gup-remove-the-restriction-on-locked-with-foll_longterm.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-gup-remove-the-restriction-on-locked-with-foll_longterm.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Jason Gunthorpe <jgg@xxxxxxxxxx>
Subject: mm/gup: remove the restriction on locked with FOLL_LONGTERM
Date: Wed, 16 Nov 2022 16:07:09 -0400
This restriction was created because FOLL_LONGTERM used to scan the vma
list, so it could not tolerate becoming unlocked. That was fixed in
commit 52650c8b466b ("mm/gup: remove the vma allocation from
gup_longterm_locked()") and the restriction on !vma was removed.
However, the locked restriction remained, even though it isn't necessary
anymore.
Adjust __gup_longterm_locked() so it can handle the mmap_read_lock()
becoming unlocked while it is looping for migration. Migration does not
require the mmap_read_sem because it is only handling struct pages. If we
had to unlock then ensure the whole thing returns unlocked.
Remove __get_user_pages_remote() and __gup_longterm_unlocked(). These
cases can now just directly call other functions.
Link: https://lkml.kernel.org/r/0-v1-b9ae39aa8884+14dbb-gup_longterm_locked_jgg@xxxxxxxxxx
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 109 +++++++++++++----------------------------------------
1 file changed, 27 insertions(+), 82 deletions(-)
--- a/mm/gup.c~mm-gup-remove-the-restriction-on-locked-with-foll_longterm
+++ a/mm/gup.c
@@ -1982,14 +1982,19 @@ static long __gup_longterm_locked(struct
unsigned long nr_pages,
struct page **pages,
struct vm_area_struct **vmas,
+ int *locked,
unsigned int gup_flags)
{
+ bool must_unlock = false;
unsigned int flags;
long rc, nr_pinned_pages;
+ if (locked && WARN_ON_ONCE(!*locked))
+ return -EINVAL;
+
if (!(gup_flags & FOLL_LONGTERM))
return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
- NULL, gup_flags);
+ locked, gup_flags);
/*
* If we get to this point then FOLL_LONGTERM is set, and FOLL_LONGTERM
@@ -2003,8 +2008,13 @@ static long __gup_longterm_locked(struct
return -EINVAL;
flags = memalloc_pin_save();
do {
+ if (locked && !*locked) {
+ mmap_read_lock(mm);
+ must_unlock = true;
+ *locked = 1;
+ }
nr_pinned_pages = __get_user_pages_locked(mm, start, nr_pages,
- pages, vmas, NULL,
+ pages, vmas, locked,
gup_flags);
if (nr_pinned_pages <= 0) {
rc = nr_pinned_pages;
@@ -2014,6 +2024,10 @@ static long __gup_longterm_locked(struct
} while (rc == -EAGAIN);
memalloc_pin_restore(flags);
+ if (locked && *locked && must_unlock) {
+ mmap_read_unlock(mm);
+ *locked = 0;
+ }
return rc ? rc : nr_pinned_pages;
}
@@ -2037,35 +2051,6 @@ static bool is_valid_gup_flags(unsigned
}
#ifdef CONFIG_MMU
-static long __get_user_pages_remote(struct mm_struct *mm,
- unsigned long start, unsigned long nr_pages,
- unsigned int gup_flags, struct page **pages,
- struct vm_area_struct **vmas, int *locked)
-{
- /*
- * Parts of FOLL_LONGTERM behavior are incompatible with
- * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
- * vmas. However, this only comes up if locked is set, and there are
- * callers that do request FOLL_LONGTERM, but do not set locked. So,
- * allow what we can.
- */
- if (gup_flags & FOLL_LONGTERM) {
- if (WARN_ON_ONCE(locked))
- return -EINVAL;
- /*
- * This will check the vmas (even if our vmas arg is NULL)
- * and return -ENOTSUPP if DAX isn't allowed in this case:
- */
- return __gup_longterm_locked(mm, start, nr_pages, pages,
- vmas, gup_flags | FOLL_TOUCH |
- FOLL_REMOTE);
- }
-
- return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
- locked,
- gup_flags | FOLL_TOUCH | FOLL_REMOTE);
-}
-
/**
* get_user_pages_remote() - pin user pages in memory
* @mm: mm_struct of target mm
@@ -2134,8 +2119,8 @@ long get_user_pages_remote(struct mm_str
if (!is_valid_gup_flags(gup_flags))
return -EINVAL;
- return __get_user_pages_remote(mm, start, nr_pages, gup_flags,
- pages, vmas, locked);
+ return __gup_longterm_locked(mm, start, nr_pages, pages, vmas, locked,
+ gup_flags | FOLL_TOUCH | FOLL_REMOTE);
}
EXPORT_SYMBOL(get_user_pages_remote);
@@ -2147,14 +2132,6 @@ long get_user_pages_remote(struct mm_str
{
return 0;
}
-
-static long __get_user_pages_remote(struct mm_struct *mm,
- unsigned long start, unsigned long nr_pages,
- unsigned int gup_flags, struct page **pages,
- struct vm_area_struct **vmas, int *locked)
-{
- return 0;
-}
#endif /* !CONFIG_MMU */
/**
@@ -2181,7 +2158,7 @@ long get_user_pages(unsigned long start,
return -EINVAL;
return __gup_longterm_locked(current->mm, start, nr_pages,
- pages, vmas, gup_flags | FOLL_TOUCH);
+ pages, vmas, NULL, gup_flags | FOLL_TOUCH);
}
EXPORT_SYMBOL(get_user_pages);
@@ -2207,18 +2184,9 @@ long get_user_pages_unlocked(unsigned lo
int locked = 1;
long ret;
- /*
- * FIXME: Current FOLL_LONGTERM behavior is incompatible with
- * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
- * vmas. As there are no users of this flag in this call we simply
- * disallow this option for now.
- */
- if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
- return -EINVAL;
-
mmap_read_lock(mm);
- ret = __get_user_pages_locked(mm, start, nr_pages, pages, NULL,
- &locked, gup_flags | FOLL_TOUCH);
+ ret = __gup_longterm_locked(mm, start, nr_pages, pages, NULL, &locked,
+ gup_flags | FOLL_TOUCH);
if (locked)
mmap_read_unlock(mm);
return ret;
@@ -2787,29 +2755,6 @@ static bool gup_fast_permitted(unsigned
}
#endif
-static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
- unsigned int gup_flags, struct page **pages)
-{
- int ret;
-
- /*
- * FIXME: FOLL_LONGTERM does not work with
- * get_user_pages_unlocked() (see comments in that function)
- */
- if (gup_flags & FOLL_LONGTERM) {
- mmap_read_lock(current->mm);
- ret = __gup_longterm_locked(current->mm,
- start, nr_pages,
- pages, NULL, gup_flags);
- mmap_read_unlock(current->mm);
- } else {
- ret = get_user_pages_unlocked(start, nr_pages,
- pages, gup_flags);
- }
-
- return ret;
-}
-
static unsigned long lockless_pages_from_mm(unsigned long start,
unsigned long end,
unsigned int gup_flags,
@@ -2893,8 +2838,8 @@ static int internal_get_user_pages_fast(
/* Slow path: try to get the remaining pages with get_user_pages */
start += nr_pinned << PAGE_SHIFT;
pages += nr_pinned;
- ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned, gup_flags,
- pages);
+ ret = get_user_pages_unlocked(start, nr_pages - nr_pinned, pages,
+ gup_flags);
if (ret < 0) {
/*
* The caller has to unpin the pages we already pinned so
@@ -3093,9 +3038,9 @@ long pin_user_pages_remote(struct mm_str
if (WARN_ON_ONCE(!pages))
return -EINVAL;
- gup_flags |= FOLL_PIN;
- return __get_user_pages_remote(mm, start, nr_pages, gup_flags,
- pages, vmas, locked);
+ return __gup_longterm_locked(mm, start, nr_pages, pages, vmas, locked,
+ gup_flags | FOLL_PIN | FOLL_TOUCH |
+ FOLL_REMOTE);
}
EXPORT_SYMBOL(pin_user_pages_remote);
@@ -3129,7 +3074,7 @@ long pin_user_pages(unsigned long start,
gup_flags |= FOLL_PIN;
return __gup_longterm_locked(current->mm, start, nr_pages,
- pages, vmas, gup_flags);
+ pages, vmas, NULL, gup_flags);
}
EXPORT_SYMBOL(pin_user_pages);
_
Patches currently in -mm which might be from jgg@xxxxxxxxxx are
mm-gup-remove-the-restriction-on-locked-with-foll_longterm.patch
