Re: [PATCH] mm/memory-failure: make sure wait for page writeback in memory_failure

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Tue, May 11, 2021 at 03:03:29PM +0800, yangerkun wrote:
> Our syzkaller trigger the "BUG_ON(!list_empty(&inode->i_wb_list))" in
> clear_inode:
> 
> [  292.016156] ------------[ cut here ]------------
> [  292.017144] kernel BUG at fs/inode.c:519!
> [  292.017860] Internal error: Oops - BUG: 0 [#1] SMP
> [  292.018741] Dumping ftrace buffer:
> [  292.019577]    (ftrace buffer empty)
> [  292.020430] Modules linked in:
> [  292.021748] Process syz-executor.0 (pid: 249, stack limit =
> 0x00000000a12409d7)
> [  292.023719] CPU: 1 PID: 249 Comm: syz-executor.0 Not tainted 4.19.95
> [  292.025206] Hardware name: linux,dummy-virt (DT)
> [  292.026176] pstate: 80000005 (Nzcv daif -PAN -UAO)
> [  292.027244] pc : clear_inode+0x280/0x2a8
> [  292.028045] lr : clear_inode+0x280/0x2a8
> [  292.028877] sp : ffff8003366c7950
> [  292.029582] x29: ffff8003366c7950 x28: 0000000000000000
> [  292.030570] x27: ffff80032b5f4708 x26: ffff80032b5f4678
> [  292.031863] x25: ffff80036ae6b300 x24: ffff8003689254d0
> [  292.032902] x23: ffff80036ae69d80 x22: 0000000000033cc8
> [  292.033928] x21: 0000000000000000 x20: ffff80032b5f47a0
> [  292.034941] x19: ffff80032b5f4678 x18: 0000000000000000
> [  292.035958] x17: 0000000000000000 x16: 0000000000000000
> [  292.037102] x15: 0000000000000000 x14: 0000000000000000
> [  292.038103] x13: 0000000000000004 x12: 0000000000000000
> [  292.039137] x11: 1ffff00066cd8f52 x10: 1ffff00066cd8ec8
> [  292.040216] x9 : dfff200000000000 x8 : ffff10006ac1e86a
> [  292.041432] x7 : dfff200000000000 x6 : ffff100066cd8f1e
> [  292.042516] x5 : dfff200000000000 x4 : ffff80032b5f47a0
> [  292.043525] x3 : ffff200008000000 x2 : ffff200009867000
> [  292.044560] x1 : ffff8003366bb000 x0 : 0000000000000000
> [  292.045569] Call trace:
> [  292.046083]  clear_inode+0x280/0x2a8
> [  292.046828]  ext4_clear_inode+0x38/0xe8
> [  292.047593]  ext4_free_inode+0x130/0xc68
> [  292.048383]  ext4_evict_inode+0xb20/0xcb8
> [  292.049162]  evict+0x1a8/0x3c0
> [  292.049761]  iput+0x344/0x460
> [  292.050350]  do_unlinkat+0x260/0x410
> [  292.051042]  __arm64_sys_unlinkat+0x6c/0xc0
> [  292.051846]  el0_svc_common+0xdc/0x3b0
> [  292.052570]  el0_svc_handler+0xf8/0x160
> [  292.053303]  el0_svc+0x10/0x218
> [  292.053908] Code: 9413f4a9 d503201f f90017b6 97f4d5b1 (d4210000)
> [  292.055471] ---[ end trace 01b339dd07795f8d ]---
> [  292.056443] Kernel panic - not syncing: Fatal exception
> [  292.057488] SMP: stopping secondary CPUs
> [  292.058419] Dumping ftrace buffer:
> [  292.059078]    (ftrace buffer empty)
> [  292.059756] Kernel Offset: disabled
> [  292.060443] CPU features: 0x10,a1006000
> [  292.061195] Memory Limit: none
> [  292.061794] Rebooting in 86400 seconds..
> 
> Crash of this problem show that someone call __munlock_pagevec to clear
> page LRU.
> 
>  #0 [ffff80035f02f4c0] __switch_to at ffff20000808d020
>  #1 [ffff80035f02f4f0] __schedule at ffff20000985102c
>  #2 [ffff80035f02f5e0] schedule at ffff200009851d1c
>  #3 [ffff80035f02f600] io_schedule at ffff2000098525c0
>  #4 [ffff80035f02f620] __lock_page at ffff20000842d2d4
>  #5 [ffff80035f02f710] __munlock_pagevec at ffff2000084c4600
>  #6 [ffff80035f02f870] munlock_vma_pages_range at ffff2000084c5928
>  #7 [ffff80035f02fa60] do_munmap at ffff2000084cbdf4
>  #8 [ffff80035f02faf0] mmap_region at ffff2000084ce20c
>  #9 [ffff80035f02fb90] do_mmap at ffff2000084cf018
> 
> So memory_failure will call identify_page_state without
> wait_on_page_writeback. And after generic_truncate_error_page clear the
> mapping of this page. end_page_writeback won't call
> sb_clear_inode_writeback to clear inode->i_wb_list. That will trigger
> BUG_ON in clear_inode!
> 
> Fix it by move the wait_on_page_writeback before check of LRU.
> 
> Signed-off-by: yangerkun <yangerkun@huawei.com>

The if-block of "goto identify_page_state" was introduced by commit
0bc1f8b0682c ("hwpoison: fix the handling path of the victimized page frame
that belong to non-LRU"), and maybe the issue got visible on commit
6c60d2b5746c ("fs/fs-writeback.c: add a new writeback list for sync"),
which added inode->i_wb_list.
So you can add Fixes tag for either commit (maybe 0bc1f8b0682c?).

Thanks,
Naoya Horiguchi

> ---
>  mm/memory-failure.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index bd3945446d47..9870a22800d9 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1527,15 +1527,15 @@ int memory_failure(unsigned long pfn, int flags)
>  		return 0;
>  	}
>  
> -	if (!PageTransTail(p) && !PageLRU(p))
> -		goto identify_page_state;
> -
>  	/*
>  	 * It's very difficult to mess with pages currently under IO
>  	 * and in many cases impossible, so we just avoid it here.
>  	 */
>  	wait_on_page_writeback(p);
>  
> +	if (!PageTransTail(p) && !PageLRU(p))
> +		goto identify_page_state;
> +
>  	/*
>  	 * Now take care of user space mappings.
>  	 * Abort on fail: __delete_from_page_cache() assumes unmapped page.
> -- 
> 2.25.4
>