mm, thp: bail out early in collapse_file for writeback page

commit 74c42e1 upstream.

Currently collapse_file does not explicitly check PG_writeback, instead,
page_has_private and try_to_release_page are used to filter writeback
pages.  This does not work for xfs with blocksize equal to or larger
than pagesize, because in such case xfs has no page->private.

This makes collapse_file bail out early for writeback page.  Otherwise,
xfs end_page_writeback will panic as follows.

  page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:ffff0003f88c86a8 index:0x0 pfn:0x84ef32
  aops:xfs_address_space_operations [xfs] ino:30000b7 dentry name:"libtest.so"
  flags: 0x57fffe0000008027(locked|referenced|uptodate|active|writeback)
  raw: 57fffe0000008027 ffff80001b48bc28 ffff80001b48bc28 ffff0003f88c86a8
  raw: 0000000000000000 0000000000000000 00000000ffffffff ffff0000c3e9a000
  page dumped because: VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u))
  page->mem_cgroup:ffff0000c3e9a000
  ------------[ cut here ]------------
  kernel BUG at include/linux/mm.h:1212!
  Internal error: Oops - BUG: 0 [#1] SMP
  Modules linked in:
  BUG: Bad page state in process khugepaged  pfn:84ef32
   xfs(E)
  page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:0 index:0x0 pfn:0x84ef32
   libcrc32c(E) rfkill(E) aes_ce_blk(E) crypto_simd(E) ...
  CPU: 25 PID: 0 Comm: swapper/25 Kdump: loaded Tainted: ...
  pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--)
  Call trace:
    end_page_writeback+0x1c0/0x214
    iomap_finish_page_writeback+0x13c/0x204
    iomap_finish_ioend+0xe8/0x19c
    iomap_writepage_end_bio+0x38/0x50
    bio_endio+0x168/0x1ec
    blk_update_request+0x278/0x3f0
    blk_mq_end_request+0x34/0x15c
    virtblk_request_done+0x38/0x74 [virtio_blk]
    blk_done_softirq+0xc4/0x110
    __do_softirq+0x128/0x38c
    __irq_exit_rcu+0x118/0x150
    irq_exit+0x1c/0x30
    __handle_domain_irq+0x8c/0xf0
    gic_handle_irq+0x84/0x108
    el1_irq+0xcc/0x180
    arch_cpu_idle+0x18/0x40
    default_idle_call+0x4c/0x1a0
    cpuidle_idle_call+0x168/0x1e0
    do_idle+0xb4/0x104
    cpu_startup_entry+0x30/0x9c
    secondary_start_kernel+0x104/0x180
  Code: d4210000 b0006161 910c8021 94013f4d (d4210000)
  ---[ end trace 4a88c6a074082f8c ]---
  Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 99cb0db ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by: Rongwei Wang <[email protected]>
Signed-off-by: Xu Yu <[email protected]>
Suggested-by: Yang Shi <[email protected]>
Reviewed-by: Matthew Wilcox (Oracle) <[email protected]>
Reviewed-by: Yang Shi <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Cc: Song Liu <[email protected]>
Cc: William Kucharski <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: wangrongwei

mm/khugepaged.c

@@ -1758,6 +1758,10 @@ static void collapse_file(struct mm_struct *mm,
 				filemap_flush(mapping);
 				result = SCAN_FAIL;
 				goto xa_unlocked;
+			} else if (PageWriteback(page)) {
+				xas_unlock_irq(&xas);
+				result = SCAN_FAIL;
+				goto xa_unlocked;
 			} else if (trylock_page(page)) {
 				get_page(page);
 				xas_unlock_irq(&xas);
@@ -1793,7 +1797,8 @@ static void collapse_file(struct mm_struct *mm,
 			goto out_unlock;
 		}
 
-		if (!is_shmem && PageDirty(page)) {
+		if (!is_shmem && (PageDirty(page) ||
+				  PageWriteback(page))) {
 			/*
 			 * khugepaged only works on read-only fd, so this
 			 * page is dirty because it hasn't been flushed