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SubjectRe: [PATCH] ext4: fix memory leak in ext4_fill_super
On Thu, 29 Apr 2021 17:41:12 -0400
"Theodore Ts'o" <tytso@mit.edu> wrote:

> On Thu, Apr 29, 2021 at 11:09:56PM +0300, Pavel Skripkin wrote:
> > > we will exit with -ENOMEM. So at the very least all callers of
> > > kthread_stop() also need to check for -ENOMEM as well as -EINTR
> > > --- or, be somehow sure that the thread function was successfully
> > > called and started. In this particular case, the ext4 mount code
> > > had just started the kmmpd thread, and then detected that
> > > something else had gone wrong, and failed the mount before the
> > > kmmpd thread ever had a chance to run.
> >
> > There is a small problem about -ENOMEM...
>
> What I'd suggest is that we simply move
>
> > exit_thread:
> > EXT4_SB(sb)->s_mmp_tsk = NULL;
> > kfree(data);
> > brelse(bh);
> > return retval;
> > }
>
> out of the thread function. That means hanging struct mmpd_data off
> the struct ext4_sb_info structure, and then adding a function like
> this to fs/ext4/mmp.c
>
> static void ext4_stop_mmpd(struct ext4_sb_info *sbi)
> {
> if (sbi->s_mmp_tsk) {
> kthread_stop(sbi->s_mmp_tsk);
> brelse(sbi->s_mmp_data->bh);
> kfree(sbi->s_mmp_data);
> sbi->s_mmp_data = NULL;
> sbi->s_mmp_tsk = NULL;
> }
> }
>
> Basically, just move all of the cleanup so it is done after the
> kthread is stopped, so we don't have to do any fancy error checking.
> We just do it unconditionally.

This sound much better than my idea. Will do it in v2.

Thanks!

>
> - Ted
>
> P.S. Actually, we could drop the struct mmpd_data altogether, and
> just hang the buffer head as sbi->s_mmp_bh. Then we can just pass the
> struct super * as the private pointer to kmmpd().
>



With regards,
Pavel Skripkin

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