Syz Test if issue still reproduce

Shivank Garg
2025-04-30T05:12:45Z

Hi,

Testing if this issue https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
still reproduces

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 33035b665

diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
index df575a873ec6..f863ba521533 100644
--- a/fs/jfs/jfs_metapage.c
+++ b/fs/jfs/jfs_metapage.c
@@ -15,6 +15,7 @@
#include <linux/mempool.h>
#include <linux/seq_file.h>
#include <linux/writeback.h>
+#include <linux/migrate.h>
#include "jfs_incore.h"
#include "jfs_superblock.h"
#include "jfs_filsys.h"
@@ -151,6 +152,54 @@ static inline void dec_io(struct folio *folio, blk_status_t status,
handler(folio, anchor->status);
}

+static int __metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+ struct folio *src, enum migrate_mode mode)
+{
+ struct meta_anchor *src_anchor = src->private;
+ struct metapage *mps[MPS_PER_PAGE] = {0};
+ struct metapage *mp;
+ int i, rc;
+
+ for (i = 0; i < MPS_PER_PAGE; i++) {
+ mp = src_anchor->mp[i];
+ if (mp && metapage_locked(mp))
+ return -EAGAIN;
+ }
+
+ rc = filemap_migrate_folio(mapping, dst, src, mode);
+ if (rc != MIGRATEPAGE_SUCCESS)
+ return rc;
+
+ for (i = 0; i < MPS_PER_PAGE; i++) {
+ mp = src_anchor->mp[i];
+ if (!mp)
+ continue;
+ if (unlikely(insert_metapage(dst, mp))) {
+ /* If error, roll-back previosly inserted pages */
+ for (int j = 0 ; j < i; j++) {
+ if (mps[j])
+ remove_metapage(dst, mps[j]);
+ }
+ return -EAGAIN;
+ }
+ mps[i] = mp;
+ }
+
+ /* Update the metapage and remove it from src */
+ for (i = 0; i < MPS_PER_PAGE; i++) {
+ mp = mps[i];
+ if (mp) {
+ int page_offset = mp->data - folio_address(src);
+
+ mp->data = folio_address(dst) + page_offset;
+ mp->folio = dst;
+ remove_metapage(src, mp);
+ }
+ }
+
+ return MIGRATEPAGE_SUCCESS;
+}
+
#else
static inline struct metapage *folio_to_mp(struct folio *folio, int offset)
{
@@ -175,6 +224,32 @@ static inline void remove_metapage(struct folio *folio, struct metapage *mp)
#define inc_io(folio) do {} while(0)
#define dec_io(folio, status, handler) handler(folio, status)

+static int __metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+ struct folio *src, enum migrate_mode mode)
+{
+ struct metapage *mp;
+ int page_offset;
+ int rc;
+
+ mp = folio_to_mp(src, 0);
+ if (mp && metapage_locked(mp))
+ return -EAGAIN;
+
+ rc = filemap_migrate_folio(mapping, dst, src, mode);
+ if (rc != MIGRATEPAGE_SUCCESS)
+ return rc;
+
+ if (unlikely(insert_metapage(dst, mp)))
+ return -EAGAIN;
+
+ page_offset = mp->data - folio_address(src);
+ mp->data = folio_address(dst) + page_offset;
+ mp->folio = dst;
+ remove_metapage(src, mp);
+
+ return MIGRATEPAGE_SUCCESS;
+}
+
#endif

static inline struct metapage *alloc_metapage(gfp_t gfp_mask)
@@ -554,6 +629,24 @@ static bool metapage_release_folio(struct folio *folio, gfp_t gfp_mask)
return ret;
}

+/**
+ * metapage_migrate_folio - Migration function for JFS metapages
+ */
+static int metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+ struct folio *src, enum migrate_mode mode)
+{
+ int expected_count;
+
+ if (!src->private)
+ return filemap_migrate_folio(mapping, dst, src, mode);
+
+ /* Check whether page does not have extra refs before we do more work */
+ expected_count = folio_expected_ref_count(src) + 1;
+ if (folio_ref_count(src) != expected_count)
+ return -EAGAIN;
+ return __metapage_migrate_folio(mapping, dst, src, mode);
+}
+
static void metapage_invalidate_folio(struct folio *folio, size_t offset,
size_t length)
{
@@ -570,6 +663,7 @@ const struct address_space_operations jfs_metapage_aops = {
.release_folio = metapage_release_folio,
.invalidate_folio = metapage_invalidate_folio,
.dirty_folio = filemap_dirty_folio,
+ .migrate_folio = metapage_migrate_folio,
};

struct metapage *__get_metapage(struct inode *inode, unsigned long lblock,
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 68d3dd14b323..1db540bb9381 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2115,6 +2115,61 @@ static inline bool folio_maybe_mapped_shared(struct folio *folio)
return folio_test_large_maybe_mapped_shared(folio);
}

+/**
+ * folio_expected_ref_count - calculate the expected folio refcount
+ * @folio: the folio
+ *
+ * Calculate the expected folio refcount, taking references from the pagecache,
+ * swapcache, PG_private and page table mappings into account. Useful in
+ * combination with folio_ref_count() to detect unexpected references (e.g.,
+ * GUP or other temporary references).
+ *
+ * Does currently not consider references from the LRU cache. If the folio
+ * was isolated from the LRU (which is the case during migration or split),
+ * the LRU cache does not apply.
+ *
+ * Calling this function on an unmapped folio -- !folio_mapped() -- that is
+ * locked will return a stable result.
+ *
+ * Calling this function on a mapped folio will not result in a stable result,
+ * because nothing stops additional page table mappings from coming (e.g.,
+ * fork()) or going (e.g., munmap()).
+ *
+ * Calling this function without the folio lock will also not result in a
+ * stable result: for example, the folio might get dropped from the swapcache
+ * concurrently.
+ *
+ * However, even when called without the folio lock or on a mapped folio,
+ * this function can be used to detect unexpected references early (for example,
+ * if it makes sense to even lock the folio and unmap it).
+ *
+ * The caller must add any reference (e.g., from folio_try_get()) it might be
+ * holding itself to the result.
+ *
+ * Returns the expected folio refcount.
+ */
+static inline int folio_expected_ref_count(const struct folio *folio)
+{
+ const int order = folio_order(folio);
+ int ref_count = 0;
+
+ if (WARN_ON_ONCE(folio_test_slab(folio)))
+ return 0;
+
+ if (folio_test_anon(folio)) {
+ /* One reference per page from the swapcache. */
+ ref_count += folio_test_swapcache(folio) << order;
+ } else if (!((unsigned long)folio->mapping & PAGE_MAPPING_FLAGS)) {
+ /* One reference per page from the pagecache. */
+ ref_count += !!folio->mapping << order;
+ /* One reference from PG_private. */
+ ref_count += folio_test_private(folio);
+ }
+
+ /* One reference per page table mapping. */
+ return ref_count + folio_mapcount(folio);
+}
+
#ifndef HAVE_ARCH_MAKE_FOLIO_ACCESSIBLE
static inline int arch_make_folio_accessible(struct folio *folio)
{
diff --git a/mm/migrate.c b/mm/migrate.c
index c80591514e66..67f2bf1eb51e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -445,20 +445,6 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
}
#endif

-static int folio_expected_refs(struct address_space *mapping,
- struct folio *folio)
-{
- int refs = 1;
- if (!mapping)
- return refs;
-
- refs += folio_nr_pages(folio);
- if (folio_test_private(folio))
- refs++;
-
- return refs;
-}
-
/*
* Replace the folio in the mapping.
*
@@ -601,7 +587,7 @@ static int __folio_migrate_mapping(struct address_space *mapping,
int folio_migrate_mapping(struct address_space *mapping,
struct folio *newfolio, struct folio *folio, int extra_count)
{
- int expected_count = folio_expected_refs(mapping, folio) + extra_count;
+ int expected_count = folio_expected_ref_count(folio) + extra_count + 1;

if (folio_ref_count(folio) != expected_count)
return -EAGAIN;
@@ -618,7 +604,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
struct folio *dst, struct folio *src)
{
XA_STATE(xas, &mapping->i_pages, folio_index(src));
- int rc, expected_count = folio_expected_refs(mapping, src);
+ int rc, expected_count = folio_expected_ref_count(src) + 1;

if (folio_ref_count(src) != expected_count)
return -EAGAIN;
@@ -749,7 +735,7 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
struct folio *src, void *src_private,
enum migrate_mode mode)
{
- int rc, expected_count = folio_expected_refs(mapping, src);
+ int rc, expected_count = folio_expected_ref_count(src) + 1;

/* Check whether src does not have extra refs before we do more work */
if (folio_ref_count(src) != expected_count)
@@ -837,7 +823,7 @@ static int __buffer_migrate_folio(struct address_space *mapping,
return migrate_folio(mapping, dst, src, mode);

/* Check whether page does not have extra refs before we do more work */
- expected_count = folio_expected_refs(mapping, src);
+ expected_count = folio_expected_ref_count(src) + 1;
if (folio_ref_count(src) != expected_count)
return -EAGAIN;