linux-ext4 - Re: [PATCH] ext2: do not sleep in ext2

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Message-ID: <20210916094836.GD10610@quack2.suse.cz>
Date:   Thu, 16 Sep 2021 11:48:36 +0200
From:   Jan Kara <jack@...e.cz>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>, Jan Kara <jack@...e.com>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] ext2: do not sleep in ext2_error()

On Fri 03-09-21 08:48:38, Theodore Ts'o wrote:
> On Fri, Sep 03, 2021 at 12:05:38PM +0300, Dan Carpenter wrote:
> > No one expects error logging functions to sleep so sometimes they are
> > called with spinlocks held.  In this case the problematic call tree is:
> > 
> > ext2_statfs() <- disables preempt
> > -> ext2_count_free_inodes()
> >    -> ext2_get_group_desc()
> >       -> ext2_error()
> > 
> > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > ---
> > This is just from static analysis.  NOT TESTED!
> > 
> > Probably a safer fix would be to just call pr_err() instead of
> > ext2_error() in ext2_get_group_desc().  I can send that fix instead if
> > people want.
> 
> Looking at both of the ext2_error() calls in ext2_get_group_desc(),
> those are really more in the way of assertions rather than warning of
> an on-disk corruption issue.  The second "group descriptor not loaded"
> should never happen, and the "block_group >= groups_count" should have
> been caught via an invalid block number or check by the caller (or an
> outright code bug in say ext2_statfs().
> 
> So I suspect both of those would be more usefule as a WARN() rather
> than a call to ext2_error(), since stack trace would actually provide
> more useful data to root causing the issue.  Jan, what do you think?

Yes, I agree. Definitely better than not flushing error on other
ext2_error() calls. BTW, Dan, I don't see a patch with WARN() in my inbox.
Did it get lost somewhere?

								Honza

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