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    SubjectRe: [PATCH v2] ext4: set csum seed in tmp inode while migrating to extents
    On Tue, Dec 14, 2021 at 05:50:58PM +0000, Luís Henriques wrote:
    > When migrating to extents, the temporary inode will have it's own checksum
    > seed. This means that, when swapping the inodes data, the inode checksums
    > will be incorrect.
    >
    > This can be fixed by recalculating the extents checksums again. Or simply
    > by copying the seed into the temporary inode.
    >
    > Link: https://bugzilla.kernel.org/show_bug.cgi?id=213357
    > Reported-by: Jeroen van Wolffelaar <jeroen@wolffelaar.nl>
    > Signed-off-by: Luís Henriques <lhenriques@suse.de>
    > ---
    > fs/ext4/migrate.c | 12 +++++++++++-
    > 1 file changed, 11 insertions(+), 1 deletion(-)
    >
    > changes since v1:
    >
    > * Dropped tmp_ei variable
    > * ->i_csum_seed is now initialised immediately after tmp_inode is created
    > * New comment about the seed initialization and stating that recovery
    > needs to be fixed.
    >
    > Cheers,
    > --
    > Luís
    >
    > diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
    > index 7e0b4f81c6c0..36dfc88ce05b 100644
    > --- a/fs/ext4/migrate.c
    > +++ b/fs/ext4/migrate.c
    > @@ -459,6 +459,17 @@ int ext4_ext_migrate(struct inode *inode)
    > ext4_journal_stop(handle);
    > goto out_unlock;
    > }
    > + /*
    > + * Use the correct seed for checksum (i.e. the seed from 'inode'). This
    > + * is so that the metadata blocks will have the correct checksum after
    > + * the migration.
    > + *
    > + * Note however that, if a crash occurs during the migration process,
    > + * the recovery process is broken because the tmp_inode checksums will
    > + * be wrong and the orphans cleanup will fail.

    ...and then what does the user do?

    --D

    > + */
    > + ei = EXT4_I(inode);
    > + EXT4_I(tmp_inode)->i_csum_seed = ei->i_csum_seed;
    > i_size_write(tmp_inode, i_size_read(inode));
    > /*
    > * Set the i_nlink to zero so it will be deleted later
    > @@ -502,7 +513,6 @@ int ext4_ext_migrate(struct inode *inode)
    > goto out_tmp_inode;
    > }
    >
    > - ei = EXT4_I(inode);
    > i_data = ei->i_data;
    > memset(&lb, 0, sizeof(lb));
    >

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