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Subject: Re: [RFC PATCH] gfs2: Fix missing cleanup quota in gfs2_put_super()
CC:     <liwei391@huawei.com>, <rpeterso@redhat.com>,
        <agruenba@redhat.com>, <cluster-devel@redhat.com>,
        <syzkaller-bugs@googlegroups.com>, <linux-kernel@vger.kernel.org>
References: <20221201115032.3540859-1-bobo.shaobowang@huawei.com>
From:   "Wangshaobo (bobo)" <bobo.shaobowang@huawei.com>
Message-ID: <5c66dbe3-5701-ba42-7933-73a31c2dc891@huawei.com>
Date:   Sat, 3 Dec 2022 15:28:00 +0800
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?? 2022/12/1 19:50, Wang ShaoBo д??:
> syzbot has reported an interesting issue:
> 
> INFO: task syz-executor888:3126 blocked for more than 143 seconds.
>        Not tainted 6.1.0-rc6-syzkaller-32662-g6d464646530f #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:syz-executor888 state:D stack:0     pid:3126  ppid:3124   flags:0x00000000
> Call trace:
>   __switch_to+0x180/0x298 arch/arm64/kernel/process.c:553
>   context_switch kernel/sched/core.c:5209 [inline]
>   __schedule+0x408/0x594 kernel/sched/core.c:6521
>   schedule+0x64/0xa4 kernel/sched/core.c:6597
>   schedule_timeout+0x108/0x1b4 kernel/time/timer.c:1935
>   gfs2_gl_hash_clear+0xd4/0x1b0 fs/gfs2/glock.c:2263
>   gfs2_put_super+0x318/0x390 fs/gfs2/super.c:620
>   generic_shutdown_super+0x94/0x198 fs/super.c:492
>   kill_block_super+0x30/0x78 fs/super.c:1428
>   gfs2_kill_sb+0x68/0x78
>   deactivate_locked_super+0x70/0xe8 fs/super.c:332
>   deactivate_super+0xd0/0xd4 fs/super.c:363
>   cleanup_mnt+0x184/0x1c0 fs/namespace.c:1186
>   __cleanup_mnt+0x20/0x30 fs/namespace.c:1193
>   task_work_run+0x100/0x148 kernel/task_work.c:179
>   resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
>   do_notify_resume+0x174/0x1f0 arch/arm64/kernel/signal.c:1127
>   prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
>   exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
>   el0_svc+0x9c/0x150 arch/arm64/kernel/entry-common.c:638
>   el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
>   el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584
> 
> Showing all locks held in the system:
> 1 lock held by rcu_tasks_kthre/11:
>   #0: ffff80000d4a4768 (rcu_tasks.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x3c/0x450 kernel/rcu/tasks.h:507
> 1 lock held by rcu_tasks_trace/12:
>   #0: ffff80000d4a4db8 (rcu_tasks_trace.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x3c/0x450 kernel/rcu/tasks.h:507
> 1 lock held by khungtaskd/27:
>   #0: ffff80000d4a4640 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x4/0x48 include/linux/rcupdate.h:303
> 2 locks held by getty/2759:
>   #0: ffff0000c7d7e098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x28/0x58 drivers/tty/tty_ldisc.c:244
>   #1: ffff80000f6be2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x19c/0x89c drivers/tty/n_tty.c:2177
> 1 lock held by syz-executor888/3126:
>   #0: ffff0000cae680e0 (&type->s_umount_key#41){+.+.}-{3:3}, at: deactivate_super+0xc8/0xd4 fs/super.c:362
> 
> =============================================
> 
> One task blocked after executing gfs2_gl_hash_clear(), it looks
> like go to sleep for waiting the condition (&sdp->sd_glock_disposal == 0),
> this field sd_glock_disposal is used to count the getting times
> that calling gfs2_glock_get() success, In most cases, when we operate
> the mount interface, we will finally call this function:
> 
>                                do_mount()
>                                path_mount()
>                                vfs_get_tree()
>                                gfs2_get_tree()
>                                get_tree_bdev()
>                                gfs2_fill_super()
>                       ________ init_inodes()_____________
>                      V                                   V
>         gfs2_lookup_simple()                         gfs2_rindex_update()
>         gfs2_lookupi()                               gfs2_ri_update()
>         gfs2_dir_search()                         -> read_rindex_entry() //*gfs2_rgrpd->rd_gl
>      -> gfs2_inode_lookup() //*gfs2_inode->i_gl  |__ gfs2_glock_get()
>     |__gfs2_glock_get()
> 
> Correspondingly, release this glock's reference and decrease
> sdp->sd_glock_disposal through this path when umount:
> 
>                                cleanup_mnt()
>                                deactivate_super()
>                                deactivate_locked_super()
>                                gfs2_kill_sb()
>                                kill_block_super()
>                                generic_shutdown_super()
>            _gfs2_rgrpd->rd_gl__gfs2_put_super()__gfs2_inode->i_gl__
>           V                                                        V
> 	gfs2_clear_rgrpd()                           gfs2_put_super()
> 	gfs2_glock_put()                             iput()
>          gfs2_glock_free()                            evict()
>                                                       gfs2_evict_inode()
>                                                       gfs2_glock_put_eventually()
>                                                       gfs2_glock_put()
>                                                       gfs2_glock_free()
> 
> But if calling reconfigure_super() from sysfs between mount and umount,
> this path will also take the glock lock and increase sdp->sd_glock_disposal
> as it also call gfs2_glock_get():
> 
>     reconfigure_super()
>      gfs2_reconfigure()
>        gfs2_make_fs_rw() //remount filesystem read-write
>         gfs2_quota_init()
>       -> qd_alloc()      //*gfs2_quota_data->qd_gl
>      |___ gfs2_glock_get()
> 
> This relies on gfs2_quota_cleanup() that is eventually called by
> gfs2_make_fs_ro() to clean up but unfortunately the file system
> has not been remounted at this time, the condition (!sb_rdonly(sb))
> is false and gfs2_make_fs_ro() can not be called, ultimately makes
> sdp->sd_glock_disposal never be 0.
> 
> This add calling gfs2_quota_cleanup() when this filesystem remains
> readOnly, in this case we don't need sync quota or other operation
> otherwise the filesystem was really remounted.
> 
> But this modification will trigger this warning:
> 
>     WARNING: CPU: 7 PID: 2595 at include/linux/backing-dev.h:246 __folio_mark_dirty+0x559/0x7b0
I paste wrong, the warning is:
gfs2: fsid=mounts.0: warning: assertion "!qd->qd_change" failed at 
function = gfs2_quota_cleanup, file = fs/gfs2/quota.c, line = 1474

qd->qd_change has been changed in gfs2_quota_init(), but it looks
we don't need to do anything before remounting the file system as 
read-write.
> 
> We can filter this warning with adding a parameter as it doesn't
> really make sense here.
> 
> Fixes: 9e6e0a128bca ("GFS2: Merge mount.c and ops_super.c into super.c")
> Reported-by: syzbot+ed7d0f71a89e28557a77@syzkaller.appspotmail.com
> Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
> ---
>   fs/gfs2/super.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
> index b018957a1bb2..9a3c6da8db55 100644
> --- a/fs/gfs2/super.c
> +++ b/fs/gfs2/super.c
> @@ -586,7 +586,10 @@ static void gfs2_put_super(struct super_block *sb)
>   
>   	if (!sb_rdonly(sb)) {
>   		gfs2_make_fs_ro(sdp);
> +	} else {
> +		gfs2_quota_cleanup(sdp);
>   	}
> +
>   	WARN_ON(gfs2_withdrawing(sdp));
>   
>   	/*  At this point, we're through modifying the disk  */
>