在 2021/8/25 18:25, Jan Kara 写道:
Hello Kun! On Wed 25-08-21 10:13:03, yangerkun wrote:There is a question about 2d01ddc86606 ("ext4: save error info to sb through journal if available"). This commit describe that we can have checksum failure with follow case: 1. ext4_handle_error will call ext4_commit_super which write directly to the superblock 2. At the same time, jounalled update of the superblock is ongoing However, after commit 05c2c00f3769 ("ext4: protect superblock modifications with a buffer lock"), all the update for superblock and the csum will be protected with buffer lock. It seems we won't get a csum error after that commit and the journal logic in flush_stashed_error_work seems useless. Maybe there is something missing... Can you help to explain more for that...You are correct that after commit 05c2c00f3769 the checksum will be correct. However there are also other problems that 2d01ddc86606 addresses and that are mentioned in the commit description like "writing inconsistent information". The fundamental problem is that you cannot mix journalled and non-journalled updates to any block. Because e.g. the unjournalled update could store to disk information that was changed only as part of the currently running transaction and if the machine crashes before the transaction commits, we have too new information in the block and thus inconsistent filesystem. Or in the other direction, journal replay can overwrite unjournalled modifications to the superblock if we crash at the right moment.
Got it! Thanks for your explain!
Honza
