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Message-ID: <20250429175535.23125-2-jack@suse.cz> Date: Tue, 29 Apr 2025 19:55:36 +0200 From: Jan Kara <jack@...e.cz> To: Ted Tso <tytso@....edu> Cc: <linux-ext4@...r.kernel.org>, Davidlohr Bueso <dave@...olabs.net>, Luis Chamberlain <mcgrof@...nel.org>, Jan Kara <jack@...e.cz>, kdevops@...ts.linux.dev Subject: [PATCH] ext4: Fix calculation of credits for extent tree modification 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@...olabs.net> Reported-by: Luis Chamberlain <mcgrof@...nel.org> Tested-by: kdevops@...ts.linux.dev Signed-off-by: Jan Kara <jack@...e.cz> --- 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; } -- 2.43.0
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