回复: 回复: [PATCH] f2fs: fix a race condition between f2fs_write_end_io and f2fs_del_fsync_node_entry

["Zac" <zhaowuyun@wingtech.com>]

> On 2020/6/18 10:39, Zac wrote:
> >
> >> On 2020/6/17 17:04, zhaowuyun@wingtech.com wrote:
> >>> From: Wuyun Zhao <zhaowuyun@wingtech.com>
> >>>
> >>> Under some condition, the __write_node_page will submit a page which
> is
> >> not
> >>> f2fs_in_warm_node_list and will not call f2fs_add_fsync_node_entry.
> >>> f2fs_gc continue to run to invoke f2fs_iget -> do_read_inode to read
the
> >> same node page
> >>> and set code node, which make f2fs_in_warm_node_list become true,
> >>> that will cause f2fs_bug_on in f2fs_del_fsync_node_entry when
> >> f2fs_write_end_io called.
> >> Could you please add below race condition description into commit
> >> message?
> >>
> >> - f2fs_write_end_io
> >> 					- f2fs_iget
> >> 					 - do_read_inode
> >> 					  - set_cold_node
> >> 					  recover cold node flag
> >>  - f2fs_in_warm_node_list
> >>   - is_cold_node
> >>   if node is cold, assume we have added
> >>   node to fsync_node_list during writepages()
> >>  - f2fs_del_fsync_node_entry
> >>   - f2fs_bug_on() due to node page
> >>   is not in fsync_node_list
> >
> > Ok, will add the commit message.
> >
> >> BTW, I'm curious about why we can lose cold flag for non-dir inode?
> >> any clue to reproduce this bug (I mean losing cold flag)?
> >
> > it's a f2fs image with 25600MB
> > flash this image to device
> > the device will resize it according to the userdata partition size which
is
> > about 94GB
> > the device mount the f2fs partition
> > then hit this f2fs_bug_on
> >
> > seems that the cold flag is not been set when mkfs
> 
> Ah, I guess both mkfs/sload ignores setting cold node flag for non-dir
inode,
> could you please send another patch to fix this issue?

Patch v2 has been sent.

> >
> > I think the issue is that
> >
> > 1. the node page in the storage is without cold bit
> > 2. f2fs_disable_checkpoint -> f2fs_gc -> f2fs_get_node_page, this page
> won't
> > be set cold flag
> > 3. f2fs_move_node_page -> __write_node_page to write this page
> > 4. f2fs_gc -> f2fs_iget -> do_read_inode to read this page and set cold
flag
> 
> Clear enough, thanks for your explanation. :)
> 
> Thanks,
> 
> >
> >>>
> >>> [   34.966133] Call trace:
> >>> [   34.969902]  f2fs_del_fsync_node_entry+0x100/0x108
> >>> [   34.976071]  f2fs_write_end_io+0x1e0/0x288
> >>> [   34.981539]  bio_endio+0x248/0x270
> >>> [   34.986289]  blk_update_request+0x2b0/0x4d8
> >>> [   34.991841]  scsi_end_request+0x40/0x440
> >>> [   34.997126]  scsi_io_completion+0xa4/0x748
> >>> [   35.002593]  scsi_finish_command+0xdc/0x110
> >>> [   35.008143]  scsi_softirq_done+0x118/0x150
> >>> [   35.013610]  blk_done_softirq+0x8c/0xe8
> >>> [   35.018811]  __do_softirq+0x2e8/0x578
> >>> [   35.023828]  irq_exit+0xfc/0x120
> >>> [   35.028398]  handle_IPI+0x1d8/0x330
> >>> [   35.033233]  gic_handle_irq+0x110/0x1d4
> >>> [   35.038433]  el1_irq+0xb4/0x130
> >>> [   35.042917]  kmem_cache_alloc+0x3f0/0x418
> >>> [   35.048288]  radix_tree_node_alloc+0x50/0xf8
> >>> [   35.053933]  __radix_tree_create+0xf8/0x188
> >>> [   35.059484]  __radix_tree_insert+0x3c/0x128
> >>> [   35.065035]  add_gc_inode+0x90/0x118
> >>> [   35.069967]  f2fs_gc+0x1b80/0x2d70
> >>> [   35.074718]  f2fs_disable_checkpoint+0x94/0x1d0
> >>> [   35.080621]  f2fs_fill_super+0x10c4/0x1b88
> >>> [   35.086088]  mount_bdev+0x194/0x1e0
> >>> [   35.090923]  f2fs_mount+0x40/0x50
> >>> [   35.095589]  mount_fs+0xb4/0x190
> >>> [   35.100159]  vfs_kern_mount+0x80/0x1d8
> >>> [   35.105260]  do_mount+0x478/0xf18
> >>> [   35.109926]  ksys_mount+0x90/0xd0
> >>> [   35.114592]  __arm64_sys_mount+0x24/0x38
> >>>
> >>> Signed-off-by: Wuyun Zhao <zhaowuyun@wingtech.com>
> >>
> >> Reviewed-by: Chao Yu <yuchao0@huawei.com>
> >>
> >> Thanks,
> >>
> >>> ---
> >>>  fs/f2fs/inode.c | 1 +
> >>>  1 file changed, 1 insertion(+)
> >>>
> >>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> >>> index be6ac33..0df5c8c 100644
> >>> --- a/fs/f2fs/inode.c
> >>> +++ b/fs/f2fs/inode.c
> >>> @@ -402,6 +402,7 @@ static int do_read_inode(struct inode *inode)
> >>>
> >>>  	/* try to recover cold bit for non-dir inode */
> >>>  	if (!S_ISDIR(inode->i_mode) && !is_cold_node(node_page)) {
> >>> +		f2fs_wait_on_page_writeback(node_page, NODE, true, true);
> >>>  		set_cold_node(node_page, false);
> >>>  		set_page_dirty(node_page);
> >>>  	}
> >>>
> >
> > .
> >