From: Rongwei Wang rongwei.wang@linux.alibaba.com Subject: mm, thp: bail out early in collapse_file for writeback page

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=--) pc : end_page_writeback+0x1c0/0x214 lr : end_page_writeback+0x1c0/0x214 sp : ffff800011ce3cc0 x29: ffff800011ce3cc0 x28: 0000000000000000 x27: ffff000c04608040 x26: 0000000000000000 x25: ffff000c04608040 x24: 0000000000001000 x23: ffff0003f88c8530 x22: 0000000000001000 x21: ffff0003f88c8530 x20: 0000000000000000 x19: fffffe00201bcc80 x18: 0000000000000030 x17: 0000000000000000 x16: 0000000000000000 x15: ffff000c018f9760 x14: ffffffffffffffff x13: ffff8000119d72b0 x12: ffff8000119d6ee3 x11: ffff8000117b69b8 x10: 00000000ffff8000 x9 : ffff800010617534 x8 : 0000000000000000 x7 : ffff8000114f69b8 x6 : 000000000000000f x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000400 x2 : 0000000000000000 x1 : 0000000000000000 x0 : 0000000000000000 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/20211022023052.33114-1-rongwei.wang@linux.alibaba.... Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") Signed-off-by: Rongwei Wang rongwei.wang@linux.alibaba.com Signed-off-by: Xu Yu xuyu@linux.alibaba.com Suggested-by: Yang Shi shy828301@gmail.com Reviewed-by: Matthew Wilcox (Oracle) willy@infradead.org Reviewed-by: Yang Shi shy828301@gmail.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Song Liu song@kernel.org Cc: William Kucharski william.kucharski@oracle.com Cc: Hugh Dickins hughd@google.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/khugepaged.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/mm/khugepaged.c~mm-thp-bail-out-early-in-collapse_file-for-writeback-page +++ a/mm/khugepaged.c @@ -1763,6 +1763,10 @@ static void collapse_file(struct mm_stru 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); @@ -1798,7 +1802,8 @@ static void collapse_file(struct mm_stru 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 _