mm/swapfile: replace kmap_atomic() with kmap_local_page()

kmap_atomic() has been deprecated in favor of kmap_local_page().

Therefore, replace kmap_atomic() with kmap_local_page() in swapfile.c.

kmap_atomic() is implemented like a kmap_local_page() which also disables
page-faults and preemption (the latter only in !PREEMPT_RT kernels).  The
kernel virtual addresses returned by these two API are only valid in the
context of the callers (i.e., they cannot be handed to other threads).

With kmap_local_page() the mappings are per thread and CPU local like in
kmap_atomic(); however, they can handle page-faults and can be called from
any context (including interrupts).  The tasks that call kmap_local_page()
can be preempted and, when they are scheduled to run again, the kernel
virtual addresses are restored and are still valid.

In mm/swapfile.c, the blocks of code between the mappings and un-mappings
do not depend on the above-mentioned side effects of kmap_atomic(), so
that the mere replacements of the old API with the new one is all that is
required (i.e., there is no need to explicitly call pagefault_disable()
and/or preempt_disable()).

Link: https://lkml.kernel.org/r/20231127155452.586387-1-fabio.maria.de.francesco@linux.intel.com
Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4bc70f459164147e260eeb3b669737b0df1a2b82..8be70912e298fc76a300f93d2ed4bb179e6921f5 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1495,9 +1495,9 @@ int swp_swapcount(swp_entry_t entry)
 
        do {
                page = list_next_entry(page, lru);
-               map = kmap_atomic(page);
+               map = kmap_local_page(page);
                tmp_count = map[offset];
-               kunmap_atomic(map);
+               kunmap_local(map);
 
                count += (tmp_count & ~COUNT_CONTINUED) * n;
                n *= (SWAP_CONT_MAX + 1);
@@ -3477,9 +3477,9 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
                if (!(count & COUNT_CONTINUED))
                        goto out_unlock_cont;
 
-               map = kmap_atomic(list_page) + offset;
+               map = kmap_local_page(list_page) + offset;
                count = *map;
-               kunmap_atomic(map);
+               kunmap_local(map);
 
                /*
                 * If this continuation count now has some space in it,
@@ -3529,7 +3529,7 @@ static bool swap_count_continued(struct swap_info_struct *si,
        spin_lock(&si->cont_lock);
        offset &= ~PAGE_MASK;
        page = list_next_entry(head, lru);
-       map = kmap_atomic(page) + offset;
+       map = kmap_local_page(page) + offset;
 
        if (count == SWAP_MAP_MAX)      /* initial increment from swap_map */
                goto init_map;          /* jump over SWAP_CONT_MAX checks */
@@ -3539,27 +3539,27 @@ static bool swap_count_continued(struct swap_info_struct *si,
                 * Think of how you add 1 to 999
                 */
                while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
-                       kunmap_atomic(map);
+                       kunmap_local(map);
                        page = list_next_entry(page, lru);
                        BUG_ON(page == head);
-                       map = kmap_atomic(page) + offset;
+                       map = kmap_local_page(page) + offset;
                }
                if (*map == SWAP_CONT_MAX) {
-                       kunmap_atomic(map);
+                       kunmap_local(map);
                        page = list_next_entry(page, lru);
                        if (page == head) {
                                ret = false;    /* add count continuation */
                                goto out;
                        }
-                       map = kmap_atomic(page) + offset;
+                       map = kmap_local_page(page) + offset;
 init_map:              *map = 0;               /* we didn't zero the page */
                }
                *map += 1;
-               kunmap_atomic(map);
+               kunmap_local(map);
                while ((page = list_prev_entry(page, lru)) != head) {
-                       map = kmap_atomic(page) + offset;
+                       map = kmap_local_page(page) + offset;
                        *map = COUNT_CONTINUED;
-                       kunmap_atomic(map);
+                       kunmap_local(map);
                }
                ret = true;                     /* incremented */
 
@@ -3569,21 +3569,21 @@ init_map:               *map = 0;               /* we didn't zero the page */
                 */
                BUG_ON(count != COUNT_CONTINUED);
                while (*map == COUNT_CONTINUED) {
-                       kunmap_atomic(map);
+                       kunmap_local(map);
                        page = list_next_entry(page, lru);
                        BUG_ON(page == head);
-                       map = kmap_atomic(page) + offset;
+                       map = kmap_local_page(page) + offset;
                }
                BUG_ON(*map == 0);
                *map -= 1;
                if (*map == 0)
                        count = 0;
-               kunmap_atomic(map);
+               kunmap_local(map);
                while ((page = list_prev_entry(page, lru)) != head) {
-                       map = kmap_atomic(page) + offset;
+                       map = kmap_local_page(page) + offset;
                        *map = SWAP_CONT_MAX | count;
                        count = COUNT_CONTINUED;
-                       kunmap_atomic(map);
+                       kunmap_local(map);
                }
                ret = count == COUNT_CONTINUED;
        }