Re: [PATCH] Revert "f2fs: remove non-uptodate folio from the page cache in move_data_block"

[Zhaoyang Huang]

+jaegeuk, chao

On Mon, Jun 8, 2026 at 5:10 PM zhaoyang.huang <zhaoyang.huang@xxxxxxxxxx> wrote:
>
> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
>
> This reverts commit 9609dd704725a40cd63d915f2ab6c44248a44598.
>
> The kernel panics are keeping to be reported especially when the f2fs
> partition get almost full. By investigation, we find that the reason is
> one f2fs page got freed to buddy without being deleted from LRU and the
> root cause is the race happened in [2] which is enrolled by this commit.
>
> There are 3 race processes in this scenario, please find below for their
> main activities.
>
> The changed code in move_data_block() lets the GC path evict the tail-end
> folio from the page cache through folio_end_dropbehind().  Once
> folio_unmap_invalidate() removes the folio from mapping->i_pages, the
> page-cache references for all pages in the folio are dropped.  The folio
> is then kept alive only by temporary external references, which allows a
> later split to operate on a folio whose subpages are no longer protected
> by page-cache references.
>
> After the page-cache references are gone, split_folio_to_order() can
> split the big folio into individual pages and put the resulting subpages
> back on the LRU.  For tail pages beyond EOF, split removes them from the
> page cache and drops their page-cache references.  A tail page can then
> remain on the LRU with PG_lru set while holding only the split caller's
> temporary reference.  When free_folio_and_swap_cache() drops that final
> reference, the page enters the final folio_put() release path.
>
> In parallel, folio_isolate_lru() can observe the same tail page with a
> non-zero refcount and PG_lru set.  It clears PG_lru before taking its own
> reference.  If this races with the final folio_put() from the split path,
> __folio_put() sees PG_lru already cleared and skips lruvec_del_folio().
> The page is then freed back to the allocator while its lru links are
> still present in the LRU list.  A later LRU operation on a neighboring
> page detects the stale link and reports list corruption.
>
> [1]
> [   22.486082] list_del corruption. next->prev should be fffffffec10e0ac8, but was dead000000000122. (next=fffffffec10e0a88)
> [   22.486130] ------------[ cut here ]------------
> [   22.486134] kernel BUG at lib/list_debug.c:67!
> [   22.486141] Internal error: Oops - BUG: 00000000f2000800 [#1]  SMP
> [   22.488502] Tainted: [W]=WARN, [O]=OOT_MODULE
> [   22.488506] Hardware name: Spreadtrum UMS9230 1H10 SoC (DT)
> [   22.488511] pstate: 604000c5 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [   22.488517] pc : __list_del_entry_valid_or_report+0x14c/0x154
> [   22.488531] lr : __list_del_entry_valid_or_report+0x14c/0x154
> [   22.488539] sp : ffffffc08006b830
> [   22.488542] x29: ffffffc08006b868 x28: 0000000000003020 x27: 0000000000000000
> [   22.488553] x26: 0000000000000000 x25: 0000000000000004 x24: fffffffec10e0ac0
> [   22.488564] x23: 00000000000000e8 x22: 0000000000000024 x21: dead000000000122
> [   22.488574] x20: fffffffec10e0a88 x19: fffffffec10e0ac8 x18: ffffffc080061060
> [   22.488585] x17: 20747562202c3863 x16: 6130653031636566 x15: 0000000000000058
> [   22.488595] x14: 0000000000000004 x13: ffffff80f91e0000 x12: 0000000000000003
> [   22.488605] x11: 0000000000000003 x10: 0000000000000001 x9 : ffe85721f0e25f00
> [   22.488615] x8 : ffe85721f0e25f00 x7 : 0000000000000000 x6 : 6c65645f7473696c
> [   22.488625] x5 : ffffffed39b23026 x4 : 0000000000000000 x3 : 0000000000000010
> [   22.488636] x2 : 0000000000000000 x1 : 0000000000000000 x0 : 000000000000006d
> [   22.488647] Call trace:
> [   22.488651]  __list_del_entry_valid_or_report+0x14c/0x154 (P)
> [   22.488661]  __folio_put+0x2bc/0x434
> [   22.488670]  folio_put+0x28/0x58
> [   22.488678]  do_garbage_collect+0x1a34/0x2584
> [   22.488689]  f2fs_gc+0x230/0x9b4
> [   22.488697]  f2fs_fallocate+0xb90/0xdf4
> [   22.488706]  vfs_fallocate+0x1b4/0x2bc
> [   22.488716]  __arm64_sys_fallocate+0x44/0x78
> [   22.488725]  invoke_syscall+0x58/0xe4
> [   22.488732]  do_el0_svc+0x48/0xdc
> [   22.488739]  el0_svc+0x3c/0x98
> [   22.488747]  el0t_64_sync_handler+0x20/0x130
> [   22.488754]  el0t_64_sync+0x1c4/0x1c8
>
> [2]
> CPU0 (f2fs GC)              CPU1 (split_folio_to_order)          CPU2 (folio_isolate_lru)
>
> F: pagecache refs = n
> F: extra refs = GC + split
> F: PG_lru set
> move_data_block()
> folio = f2fs_grab_cache_folio(F)
> ...
> __folio_set_dropbehind(F)
> folio_unlock(F)
> folio_end_dropbehind(F)
>   folio_unmap_invalidate(F)
>     __filemap_remove_folio(F)
>     folio_put_refs(F, n)
> folio_put(F)
>                             split_folio_to_order(F)
>                               folio_ref_freeze(F, 1)
>                               ...
>                               lru_add_split_folio(T)
>                                 list_add_tail(&T->lru, &F->lru)
>                                 folio_set_lru(T)
>                               __filemap_remove_folio(T)
>                               folio_put_refs(T, 1)
>                               /* T refcount == 1, PageLRU set */
>                                                                   folio_isolate_lru(T)
>                                                                     folio_test_clear_lru(T)
>                             free_folio_and_swap_cache(T)
>                               folio_put(T)
>                                 /* refcount: 1 -> 0 */
>                                 __folio_put(T)
>                                   __page_cache_release(T)
>                                     folio_test_lru(T) == false
>                                     /* skip lruvec_del_folio(T) */
>                                   free_frozen_pages(T)
>                                                                   folio_get(T)
>                                                                   lruvec_del_folio(T)
> later:
>   list_del(adjacent->lru)
>     next == &T->lru
>     next->prev == LIST_POISON / PCP freelist
>     BUG
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> ---
>  fs/f2fs/gc.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index ba93010924c0..3084e05e22f2 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -1468,11 +1468,7 @@ static int move_data_block(struct inode *inode, block_t bidx,
>  put_out:
>         f2fs_put_dnode(&dn);
>  out:
> -       if (!folio_test_uptodate(folio))
> -               __folio_set_dropbehind(folio);
> -       folio_unlock(folio);
> -       folio_end_dropbehind(folio);
> -       folio_put(folio);
> +       f2fs_folio_put(folio, true);
>         return err;
>  }
>
> --
> 2.25.1
>