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-rw-r--r--mm/gup.c113
1 files changed, 65 insertions, 48 deletions
diff --git a/mm/gup.c b/mm/gup.c
index c4b793385ed2..5b03d2fd3e1c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1331,8 +1331,17 @@ static bool gup_signal_pending(unsigned int flags)
}
/*
- * Please note that this function, unlike __get_user_pages will not
- * return 0 for nr_pages > 0 without FOLL_NOWAIT
+ * Locking: (*locked == 1) means that the mmap_lock has already been acquired by
+ * the caller. This function may drop the mmap_lock. If it does so, then it will
+ * set (*locked = 0).
+ *
+ * (*locked == 0) means that the caller expects this function to acquire and
+ * drop the mmap_lock. Therefore, the value of *locked will still be zero when
+ * the function returns, even though it may have changed temporarily during
+ * function execution.
+ *
+ * Please note that this function, unlike __get_user_pages(), will not return 0
+ * for nr_pages > 0, unless FOLL_NOWAIT is used.
*/
static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
unsigned long start,
@@ -1343,13 +1352,22 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
unsigned int flags)
{
long ret, pages_done;
- bool lock_dropped;
+ bool must_unlock = false;
if (locked) {
/* if VM_FAULT_RETRY can be returned, vmas become invalid */
BUG_ON(vmas);
- /* check caller initialized locked */
- BUG_ON(*locked != 1);
+ }
+
+ /*
+ * The internal caller expects GUP to manage the lock internally and the
+ * lock must be released when this returns.
+ */
+ if (locked && !*locked) {
+ if (mmap_read_lock_killable(mm))
+ return -EAGAIN;
+ must_unlock = true;
+ *locked = 1;
}
if (flags & FOLL_PIN)
@@ -1368,7 +1386,6 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
flags |= FOLL_GET;
pages_done = 0;
- lock_dropped = false;
for (;;) {
ret = __get_user_pages(mm, start, nr_pages, flags, pages,
vmas, locked);
@@ -1404,7 +1421,9 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
if (likely(pages))
pages += ret;
start += ret << PAGE_SHIFT;
- lock_dropped = true;
+
+ /* The lock was temporarily dropped, so we must unlock later */
+ must_unlock = true;
retry:
/*
@@ -1451,10 +1470,11 @@ retry:
pages++;
start += PAGE_SIZE;
}
- if (lock_dropped && *locked) {
+ if (must_unlock && *locked) {
/*
- * We must let the caller know we temporarily dropped the lock
- * and so the critical section protected by it was lost.
+ * We either temporarily dropped the lock, or the caller
+ * requested that we both acquire and drop the lock. Either way,
+ * we must now unlock, and notify the caller of that state.
*/
mmap_read_unlock(mm);
*locked = 0;
@@ -1659,9 +1679,24 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
unsigned int foll_flags)
{
struct vm_area_struct *vma;
+ bool must_unlock = false;
unsigned long vm_flags;
long i;
+ if (!nr_pages)
+ return 0;
+
+ /*
+ * The internal caller expects GUP to manage the lock internally and the
+ * lock must be released when this returns.
+ */
+ if (locked && !*locked) {
+ if (mmap_read_lock_killable(mm))
+ return -EAGAIN;
+ must_unlock = true;
+ *locked = 1;
+ }
+
/* calculate required read or write permissions.
* If FOLL_FORCE is set, we only require the "MAY" flags.
*/
@@ -1673,12 +1708,12 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
for (i = 0; i < nr_pages; i++) {
vma = find_vma(mm, start);
if (!vma)
- goto finish_or_fault;
+ break;
/* protect what we can, including chardevs */
if ((vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
!(vm_flags & vma->vm_flags))
- goto finish_or_fault;
+ break;
if (pages) {
pages[i] = virt_to_page((void *)start);
@@ -1690,9 +1725,11 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
start = (start + PAGE_SIZE) & PAGE_MASK;
}
- return i;
+ if (must_unlock && *locked) {
+ mmap_read_unlock(mm);
+ *locked = 0;
+ }
-finish_or_fault:
return i ? : -EFAULT;
}
#endif /* !CONFIG_MMU */
@@ -1861,17 +1898,13 @@ EXPORT_SYMBOL(fault_in_readable);
#ifdef CONFIG_ELF_CORE
struct page *get_dump_page(unsigned long addr)
{
- struct mm_struct *mm = current->mm;
struct page *page;
- int locked = 1;
+ int locked = 0;
int ret;
- if (mmap_read_lock_killable(mm))
- return NULL;
- ret = __get_user_pages_locked(mm, addr, 1, &page, NULL, &locked,
+ ret = __get_user_pages_locked(current->mm, addr, 1, &page, NULL,
+ &locked,
FOLL_FORCE | FOLL_DUMP | FOLL_GET);
- if (locked)
- mmap_read_unlock(mm);
return (ret == 1) ? page : NULL;
}
#endif /* CONFIG_ELF_CORE */
@@ -2047,13 +2080,9 @@ static long __gup_longterm_locked(struct mm_struct *mm,
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,
locked, gup_flags);
@@ -2070,11 +2099,6 @@ static long __gup_longterm_locked(struct mm_struct *mm,
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, locked,
gup_flags);
@@ -2085,11 +2109,6 @@ static long __gup_longterm_locked(struct mm_struct *mm,
rc = check_and_migrate_movable_pages(nr_pinned_pages, pages);
} while (rc == -EAGAIN);
memalloc_pin_restore(flags);
-
- if (locked && *locked && must_unlock) {
- mmap_read_unlock(mm);
- *locked = 0;
- }
return rc ? rc : nr_pinned_pages;
}
@@ -2242,16 +2261,10 @@ EXPORT_SYMBOL(get_user_pages);
long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
struct page **pages, unsigned int gup_flags)
{
- struct mm_struct *mm = current->mm;
- int locked = 1;
- long ret;
+ int locked = 0;
- mmap_read_lock(mm);
- ret = __gup_longterm_locked(mm, start, nr_pages, pages, NULL, &locked,
- gup_flags | FOLL_TOUCH);
- if (locked)
- mmap_read_unlock(mm);
- return ret;
+ return __gup_longterm_locked(current->mm, start, nr_pages, pages, NULL,
+ &locked, gup_flags | FOLL_TOUCH);
}
EXPORT_SYMBOL(get_user_pages_unlocked);
@@ -2904,6 +2917,7 @@ static int internal_get_user_pages_fast(unsigned long start,
{
unsigned long len, end;
unsigned long nr_pinned;
+ int locked = 0;
int ret;
if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
@@ -2932,8 +2946,9 @@ static int internal_get_user_pages_fast(unsigned long start,
/* Slow path: try to get the remaining pages with get_user_pages */
start += nr_pinned << PAGE_SHIFT;
pages += nr_pinned;
- ret = get_user_pages_unlocked(start, nr_pages - nr_pinned, pages,
- gup_flags);
+ ret = __gup_longterm_locked(current->mm, start, nr_pages - nr_pinned,
+ pages, NULL, &locked,
+ gup_flags | FOLL_TOUCH);
if (ret < 0) {
/*
* The caller has to unpin the pages we already pinned so
@@ -3183,11 +3198,13 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
/* FOLL_GET and FOLL_PIN are mutually exclusive. */
if (WARN_ON_ONCE(gup_flags & FOLL_GET))
return -EINVAL;
+ int locked = 0;
if (WARN_ON_ONCE(!pages))
return -EINVAL;
- gup_flags |= FOLL_PIN;
- return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
+ gup_flags |= FOLL_PIN | FOLL_TOUCH;
+ return __gup_longterm_locked(current->mm, start, nr_pages, pages, NULL,
+ &locked, gup_flags);
}
EXPORT_SYMBOL(pin_user_pages_unlocked);
generated by cgit (git 2.34.1) at 2024-05-10 08:47:00 +0000