Re: [PATCH 5.5 020/399] f2fs: call f2fs_balance_fs outside of locked page

From: OndÅej Jirman
Date: Sat Feb 22 2020 - 09:37:01 EST

On Sat, Feb 22, 2020 at 05:41:51AM +0100, megous hlavni wrote:
> Hello,
>
> On Fri, Feb 21, 2020 at 08:35:45AM +0100, Greg Kroah-Hartman wrote:
> > From: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> >
> > [ Upstream commit bdf03299248916640a835a05d32841bb3d31912d ]
>
> I have somes issues with this patch.
>
> It causes panics due to hung tasks on 5.6. I guess it fixes one deadlock, but
> causes other one? Not sure backporting it to stable branches is a good idea.

False alarm. The issue is unrelated to this patch.

regards,
o.

> 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
>
> > Otherwise, we can hit deadlock by waiting for the locked page in
> > move_data_block in GC.
> >
> > 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")
> > Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > ---
> > 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 33c412d178f0f..6c4436a5ce797 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);
> > --
> > 2.20.1
> >
> >
> >