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    SubjectRe: [PATCH] ext4: fix memory leak in ext4_fill_super
    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.

    - 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().

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