linux-ext4 - Re: [PATCH v4 1/2] ext4: fix inode tree inconsistency caused by ENOMEM in ext4_split_extent

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Date:   Thu, 16 Feb 2023 14:07:15 +0100
From:   Jan Kara <jack@...e.cz>
To:     zhanchengbin <zhanchengbin1@...wei.com>
Cc:     Jan Kara <jack@...e.cz>, tytso@....edu, jack@...e.com,
        linux-ext4@...r.kernel.org, yi.zhang@...wei.com,
        linfeilong@...wei.com, liuzhiqiang26@...wei.com
Subject: Re: [PATCH v4 1/2] ext4: fix inode tree inconsistency caused by
 ENOMEM in ext4_split_extent_at

On Wed 15-02-23 16:51:23, zhanchengbin wrote:
> 
> On 2023/2/14 19:48, Jan Kara wrote:
> > On Mon 13-02-23 12:05:21, zhanchengbin wrote:
> > > If ENOMEM fails when the extent is splitting, we need to restore the length
> > > of the split extent.
> > > In the call stack of the ext4_split_extent_at function, only in
> > > ext4_ext_create_new_leaf will it alloc memory and change the shape of the
> > > extent tree,even if an ENOMEM is returned at this time, the extent tree is
> > > still self-consistent, Just restore the split extent lens in the function
> > > ext4_split_extent_at.
> > > 
> > > ext4_split_extent_at
> > >   ext4_ext_insert_extent
> > >    ext4_ext_create_new_leaf
> > >     1)ext4_ext_split
> > >       ext4_find_extent
> > >     2)ext4_ext_grow_indepth
> > >       ext4_find_extent
> > > 
> > > Signed-off-by: zhanchengbin <zhanchengbin1@...wei.com>
> > > ---
> > >   fs/ext4/extents.c | 3 ++-
> > >   1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > > index 9de1c9d1a13d..0f95e857089e 100644
> > > --- a/fs/ext4/extents.c
> > > +++ b/fs/ext4/extents.c
> > > @@ -935,6 +935,7 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block,
> > >   		bh = read_extent_tree_block(inode, path[ppos].p_idx, --i, flags);
> > >   		if (IS_ERR(bh)) {
> > > +			EXT4_ERROR_INODE(inode, "IO error reading extent block");
> > 
> > Why have you added this? Usually we don't log any additional errors for IO
> > errors because the storage layer already reports it... Furthermore this
> > would potentialy panic the system / remount the fs RO which we also usually
> > don't do in case of IO errors, only in case of FS corruption.
> > 
> > 								Honza
> 
> Because failure of read_extent_tree_block indirectly leads to filesystem
> inconsistency in ext4_split_extent_at, I want the filesystem to become
> read-only after failure.

Can you please describe how exactly? Because I'd rather declare the error
directly in ext4_split_extent_at() than in ext4_find_extent() unless it
gets too complicated...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR