lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <mk5f4g4rwp37ob6qmd7asocumeepjcnufqzjvazr3yukbyzq3y@6gp6x6zvxf7r> Date: Fri, 4 Jul 2025 10:18:56 +0200 From: Jan Kara <jack@...e.cz> To: Zhang Yi <yi.zhang@...weicloud.com> Cc: Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca, ojaswin@...ux.ibm.com, sashal@...nel.org, yi.zhang@...wei.com, libaokun1@...wei.com, yukuai3@...wei.com, yangerkun@...wei.com Subject: Re: [PATCH v3 05/10] ext4: restart handle if credits are insufficient during allocating blocks On Fri 04-07-25 09:40:23, Zhang Yi wrote: > On 2025/7/4 0:27, Jan Kara wrote: > > On Thu 03-07-25 10:13:07, Zhang Yi wrote: > >> On 2025/7/2 22:18, Jan Kara wrote: > >>> On Tue 01-07-25 21:06:30, Zhang Yi wrote: > >>>> From: Zhang Yi <yi.zhang@...wei.com> > >>>> > >>>> After large folios are supported on ext4, writing back a sufficiently > >>>> large and discontinuous folio may consume a significant number of > >>>> journal credits, placing considerable strain on the journal. For > >>>> example, in a 20GB filesystem with 1K block size and 1MB journal size, > >>>> writing back a 2MB folio could require thousands of credits in the > >>>> worst-case scenario (when each block is discontinuous and distributed > >>>> across different block groups), potentially exceeding the journal size. > >>>> This issue can also occur in ext4_write_begin() and ext4_page_mkwrite() > >>>> when delalloc is not enabled. > >>>> > >>>> Fix this by ensuring that there are sufficient journal credits before > >>>> allocating an extent in mpage_map_one_extent() and > >>>> ext4_block_write_begin(). If there are not enough credits, return > >>>> -EAGAIN, exit the current mapping loop, restart a new handle and a new > >>>> transaction, and allocating blocks on this folio again in the next > >>>> iteration. > >>>> > >>>> Suggested-by: Jan Kara <jack@...e.cz> > >>>> Signed-off-by: Zhang Yi <yi.zhang@...wei.com> > >>> > >>> Very nice. Feel free to add: > >>> > >>> Reviewed-by: Jan Kara <jack@...e.cz> > >>> > >>> One small comment below: > >>> > >>>> +/* > >>>> + * Make sure that the current journal transaction has enough credits to map > >>>> + * one extent. Return -EAGAIN if it cannot extend the current running > >>>> + * transaction. > >>>> + */ > >>>> +static inline int ext4_journal_ensure_extent_credits(handle_t *handle, > >>>> + struct inode *inode) > >>>> +{ > >>>> + int credits; > >>>> + int ret; > >>>> + > >>>> + if (!handle) > >>> > >>> Shouldn't this rather be ext4_handle_valid(handle) to catch nojournal mode > >>> properly? > >>> > >> __ext4_journal_ensure_credits() already calls ext4_handle_valid() to handle > >> nojournal mode, and the '!handle' check here is to handle the case where > >> ext4_block_write_begin() passes in a NULL 'handle'. > > > > Ah, right. But then you don't need the test at all, do you? Anyway, > > whatever you decide to do with this (or nothing) is fine by me. > > > > Yeah, remove this test is fine with me. I added this one is because the > comments in ext4_handle_valid() said "Do not use this for NULL handles." > I think it is best to follow this rule. :) Right, I didn't read that comment :) So maybe the best fix will be just adding a comment before the test like: /* Called from ext4_da_write_begin() which has no handle started? */ if (!handle) return 0; Honza -- Jan Kara <jack@...e.com> SUSE Labs, CR
Powered by blists - more mailing lists