linux-kernel - Re: PROBLEM: ext4 resize2fs on-line resizing panic

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Date: Mon, 24 Jun 2024 18:53:50 +0200
From: Jan Kara <jack@...e.cz>
To: Theodore Ts'o <tytso@....edu>
Cc: Alexander Coffin <alex.coffin@...icrobots.com>,
	Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: PROBLEM: ext4 resize2fs on-line resizing panic

On Mon 24-06-24 11:26:58, Theodore Ts'o wrote:
> On Sun, Jun 23, 2024 at 06:57:13PM -0700, Alexander Coffin wrote:
> > [1.] One line summary of the problem:
> > Using resize2fs on-line resizing on a specific ext4 partition is
> > causing an Oops.
> > 
> > 
> > [6.] Output of Oops.. message (if applicable) with symbolic information
> >      resolved (see Documentation/admin-guide/bug-hunting.rst)
> > 
> > ```
> > [  445.552287] ------------[ cut here ]------------
> > [  445.552300] kernel BUG at fs/jbd2/journal.c:846!
> 
> Thanks for the bug report.  The BUG_ON is from the following assert in
> jbd2_journal_next_log_block:
> 
> 	J_ASSERT(journal->j_free > 1);
> 
> and it indicates that we ran out of space in the journal.  There are
> mechanisms to make sure that this should never happen, and if the
> journal is too small and the transaction couldn't be broken up, then
> the operation (whether it is a resize or a file truncate or some other
> operation) should have errored out, and not triggered a BUG.

Yeah, I was debugging this today and I'll shortly send a fix for JBD2 so
that we don't trigger this BUG. But the online resize will fail anyway
after my fixes (just gracefully) because the add_flex_bg() code tries to
start a transaction with more credits than the journal allows.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR