Hi, Jan! On 2025/4/30 1:55, Jan Kara wrote: > Luis and David are reporting that after running generic/750 test for 90+ > hours on 2k ext4 filesystem, they are able to trigger a warning in > jbd2_journal_dirty_metadata() complaining that there are not enough > credits in the running transaction started in ext4_do_writepages(). > > Indeed the code in ext4_do_writepages() is racy and the extent tree can > change between the time we compute credits necessary for extent tree > computation and the time we actually modify the extent tree. Thus it may > happen that the number of credits actually needed is higher. Modify > ext4_ext_index_trans_blocks() to count with the worst case of maximum > tree depth. This can reduce the possible number of writers that can > operate in the system in parallel (because the credit estimates now won't > fit in one transaction) but for reasonably sized journals this shouldn't > really be an issue. So just go with a safe and simple fix. > > Link: https://lore.kernel.org/all/20250415013641.f2ppw6wov4kn4wq2@offworld > Reported-by: Davidlohr Bueso <dave@xxxxxxxxxxxx> > Reported-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> > Tested-by: kdevops@xxxxxxxxxxxxxxx > Signed-off-by: Jan Kara <jack@xxxxxxx> This overall looks good to me now. However, the credit calculation in ext4_ext_index_trans_blocks() seems still appears to be incorrect because it does not include the leaf extent blocks. I discovered this problem while attempting to enable large folios for ext4. It can easily trigger problems when writing back a 2MB folio with a 1K block size, and each block is discontinuous. https://lore.kernel.org/linux-ext4/20241125114419.903270-7-yi.zhang@xxxxxxxxxxxxxxx/ Fortunately, this problem can only triggered after we support large folio. Reviewed-by: Zhang Yi <yi.zhang@xxxxxxxxxx> > --- > fs/ext4/extents.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c > index c616a16a9f36..43286632e650 100644 > --- a/fs/ext4/extents.c > +++ b/fs/ext4/extents.c > @@ -2396,18 +2396,19 @@ int ext4_ext_calc_credits_for_single_extent(struct inode *inode, int nrblocks, > int ext4_ext_index_trans_blocks(struct inode *inode, int extents) > { > int index; > - int depth; > > /* If we are converting the inline data, only one is needed here. */ > if (ext4_has_inline_data(inode)) > return 1; > > - depth = ext_depth(inode); > - > + /* > + * Extent tree can change between the time we estimate credits and > + * the time we actually modify the tree. Assume the worst case. > + */ > if (extents <= 1) > - index = depth * 2; > + index = EXT4_MAX_EXTENT_DEPTH * 2; > else > - index = depth * 3; > + index = EXT4_MAX_EXTENT_DEPTH * 3; > > return index; > }
