Re: [PATCH 1/6] f2fs: call f2fs_balance_fs outside of locked page

["Ondřej Jirman" <megi@xff.cz>]

Hello,

On Mon, Dec 09, 2019 at 02:23:40PM -0800, Jaegeuk Kim wrote:
> Otherwise, we can hit deadlock by waiting for the locked page in
> move_data_block in GC.

I had the task hangs on 5.6 shortly after boot. (f2fs as rootfs).
See below for stacktrace.

So I went through the changelog in f2fs and noticed this patch as
a suspect, and after reverting it the hung task panics went away.

I reverted it manually, because the master changed too much for
a clean revert:

https://megous.com/git/linux/commit/?h=orange-pi-5.6&id=9983bdae4974edc2af6ff547a401ae397388b6b5

regards,
	o.

INFO: task kworker/u16:2:341 blocked for more than 122 seconds.
      Not tainted 5.6.0-rc2-00254-g9a029a493dc16 #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u16:2   D    0   341      2 0x00000000
Workqueue: writeback wb_workfn (flush-179:0)
Backtrace:
[<c0912bd0>] (__schedule) from [<c0913274>] (schedule+0x78/0xf4)
 r10:ede1a000 r9:00000000 r8:ede1ba60 r7:ec417290 r6:00000002 r5:ede1a000
 r4:ee8e8000
[<c09131fc>] (schedule) from [<c017ec74>] (rwsem_down_write_slowpath+0x24c/0x4c0)
 r5:00000001 r4:ec417280
[<c017ea28>] (rwsem_down_write_slowpath) from [<c0915f6c>] (down_write+0x6c/0x70)
 r10:ec417280 r9:ede1bd80 r8:ee128000 r7:00000001 r6:00000000 r5:eff0afc4
 r4:ec417280
[<c0915f00>] (down_write) from [<c0435b68>] (f2fs_write_single_data_page+0x608/0x7ac)
 r5:eff0afc4 r4:ec4170e0
[<c0435560>] (f2fs_write_single_data_page) from [<c0435fc0>] (f2fs_write_cache_pages+0x2b4/0x7c4)
 r10:ede1bc28 r9:ec4171e0 r8:ec4170e0 r7:00000001 r6:ede1bd80 r5:00000001
 r4:eff0afc4
[<c0435d0c>] (f2fs_write_cache_pages) from [<c0436814>] (f2fs_write_data_pages+0x344/0x35c)
 r10:0000012c r9:ee12802c r8:ee128000 r7:00000004 r6:ec4171e0 r5:ec4170e0
 r4:ede1bd80
[<c04364d0>] (f2fs_write_data_pages) from [<c0267fa0>] (do_writepages+0x3c/0xd4)
 r10:0000012c r9:c0e03d00 r8:00001400 r7:c0264e94 r6:ede1bd80 r5:ec4171e0
 r4:ec4170e0
[<c0267f64>] (do_writepages) from [<c0310d24>] (__writeback_single_inode+0x44/0x454)
 r7:ec4171e0 r6:ede1beac r5:ede1bd80 r4:ec4170e0
[<c0310ce0>] (__writeback_single_inode) from [<c0311338>] (writeback_sb_inodes+0x204/0x4b0)
 r10:0000012c r9:c0e03d00 r8:ec417148 r7:ec4170e0 r6:ede1beac r5:ec417188
 r4:eebed848
[<c0311134>] (writeback_sb_inodes) from [<c0311634>] (__writeback_inodes_wb+0x50/0xe4)
 r10:ee7128e8 r9:c0e03d00 r8:eebed85c r7:ede1beac r6:00000000 r5:eebed848
 r4:ee120000
[<c03115e4>] (__writeback_inodes_wb) from [<c031195c>] (wb_writeback+0x294/0x338)
 r10:00020800 r9:ede1a000 r8:c0e04e64 r7:eebed848 r6:000192d0 r5:ede1beac
 r4:eebed848
[<c03116c8>] (wb_writeback) from [<c0312e98>] (wb_workfn+0x3e0/0x54c)
 r10:ee894005 r9:eebed84c r8:eebed948 r7:eebed848 r6:00000000 r5:eebed954
 r4:00002b6e
[<c0312ab8>] (wb_workfn) from [<c014f2b8>] (process_one_work+0x214/0x544)
 r10:ee894005 r9:00000200 r8:00000000 r7:ee894000 r6:ef044400 r5:edb1c700
 r4:eebed954
[<c014f0a4>] (process_one_work) from [<c014f634>] (worker_thread+0x4c/0x574)
 r10:ef044400 r9:c0e03d00 r8:ef044418 r7:00000088 r6:ef044400 r5:edb1c714
 r4:edb1c700
[<c014f5e8>] (worker_thread) from [<c01564fc>] (kthread+0x144/0x170)
 r10:ef125e90 r9:ec0f235c r8:edb1c700 r7:ede1a000 r6:00000000 r5:ec0f2300
 r4:ec0f2340
[<c01563b8>] (kthread) from [<c01010e8>] (ret_from_fork+0x14/0x2c)
Exception stack(0xede1bfb0 to 0xede1bff8)
bfa0:                                     00000000 00000000 00000000 00000000
bfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
bfe0: 00000000 00000000 00000000 00000000 00000013 00000000
 r10:00000000 r9:00000000 r8:00000000 r7:00000000 r6:00000000 r5:c01563b8
 r4:ec0f2300
NMI backtrace for cpu 2
CPU: 2 PID: 52 Comm: khungtaskd Not tainted 5.6.0-rc2-00254-g9a029a493dc16 #4
Hardware name: Allwinner A83t board
Backtrace:
[<c010db5c>] (dump_backtrace) from [<c010dee0>] (show_stack+0x20/0x24)
 r7:00000000 r6:60060013 r5:00000000 r4:c0e9ab10



>  Thread A                     Thread B
>  - do_page_mkwrite
>   - f2fs_vm_page_mkwrite
>    - lock_page
>                               - f2fs_balance_fs
>                                   - mutex_lock(gc_mutex)
>                                - f2fs_gc
>                                 - do_garbage_collect
>                                  - ra_data_block
>                                   - grab_cache_page
>    - f2fs_balance_fs
>     - mutex_lock(gc_mutex)
> 
> Fixes: 39a8695824510 ("f2fs: refactor ->page_mkwrite() flow")
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>  fs/f2fs/file.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index e7fcbd8c23f4..6cebc6681487 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -50,7 +50,7 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>  	struct page *page = vmf->page;
>  	struct inode *inode = file_inode(vmf->vma->vm_file);
>  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> -	struct dnode_of_data dn = { .node_changed = false };
> +	struct dnode_of_data dn;
>  	int err;
>  
>  	if (unlikely(f2fs_cp_error(sbi))) {
> @@ -63,6 +63,9 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>  		goto err;
>  	}
>  
> +	/* should do out of any locked page */
> +	f2fs_balance_fs(sbi, true);
> +
>  	sb_start_pagefault(inode->i_sb);
>  
>  	f2fs_bug_on(sbi, f2fs_has_inline_data(inode));
> @@ -120,8 +123,6 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>  out_sem:
>  	up_read(&F2FS_I(inode)->i_mmap_sem);
>  
> -	f2fs_balance_fs(sbi, dn.node_changed);
> -
>  	sb_end_pagefault(inode->i_sb);
>  err:
>  	return block_page_mkwrite_return(err);
> -- 
> 2.19.0.605.g01d371f741-goog
>