linux-ext4 - Re: [GIT PULL] ext2, quota, and udf fixes for 6.6-rc1

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Date:   Fri, 20 Oct 2023 10:26:26 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Shevchenko <andriy.shevchenko@...el.com>
Cc:     Baokun Li <libaokun1@...wei.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>, Jan Kara <jack@...e.cz>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Ferry Toth <ftoth@...londelft.nl>,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [GIT PULL] ext2, quota, and udf fixes for 6.6-rc1

On Fri, 20 Oct 2023 at 08:12, Andy Shevchenko
<andriy.shevchenko@...el.com> wrote:
>
> > > --- a/fs/quota/dquot.c
> > > +++ b/fs/quota/dquot.c
> > > @@ -632,8 +632,10 @@ static inline int dquot_write_dquot(struct dquot *dquot)
> > >  {
> > >         int ret = dquot->dq_sb->dq_op->write_dquot(dquot);
> > >         if (ret < 0) {
> > > +#if 0
> > >                 quota_error(dquot->dq_sb, "Can't write quota structure "
> > >                             "(error %d). Quota may get out of sync!", ret);
> > > +#endif
> > >                 /* Clear dirty bit anyway to avoid infinite loop. */
> > >                 clear_dquot_dirty(dquot);
> > >         }
>
> Doing the same on the my branch based on top of v6.6-rc6 does not help.
> So looks like a race condition somewhere happening related to that dirty bit
> (as comment states it needs to be cleaned to avoid infinite loop, that's
>  probably what happens).

Hmm. Normally, dirty bits should always be cleared *before* the
write-back, not after it. Otherwise you might lose a dirty event that
happened *during* writeback.

But I don't know the quota code.

... the fact that the #if 0 doesn't help in another case does say that
it's not the quota_error() call itself. Which it really couldn't have
been (apart from timing and compiler bugs), but it's still a data
point, I guess.

               Linus