Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Fri, 11 Nov 2022 12:44:42 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc:     dsterba@suse.cz, ChenXiaoSong <chenxiaosong2@huawei.com>,
        clm@fb.com, josef@toxicpanda.com, dsterba@suse.com,
        linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, zhangxiaoxu5@huawei.com
Subject: Re: [PATCH] btrfs: qgroup: fix sleep from invalid context bug in
 update_qgroup_limit_item()
Message-ID: <20221111114442.GK5824@twin.jikos.cz>
Reply-To: dsterba@suse.cz
References: <20221110141342.2129475-1-chenxiaosong2@huawei.com>
 <20221110205436.GJ5824@twin.jikos.cz>
 <48ac1a74-6349-ccf5-92ef-2189037122b8@gmx.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <48ac1a74-6349-ccf5-92ef-2189037122b8@gmx.com>
User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12)
Precedence: bulk

On Fri, Nov 11, 2022 at 07:31:22AM +0800, Qu Wenruo wrote:
> 
> 
> On 2022/11/11 04:54, David Sterba wrote:
> > On Thu, Nov 10, 2022 at 10:13:42PM +0800, ChenXiaoSong wrote:
> >> Syzkaller reported BUG as follows:
> >>
> >>    BUG: sleeping function called from invalid context at
> >>         include/linux/sched/mm.h:274
> >>    Call Trace:
> >>     <TASK>
> >>     dump_stack_lvl+0xcd/0x134
> >>     __might_resched.cold+0x222/0x26b
> >>     kmem_cache_alloc+0x2e7/0x3c0
> >>     update_qgroup_limit_item+0xe1/0x390
> >>     btrfs_qgroup_inherit+0x147b/0x1ee0
> >>     create_subvol+0x4eb/0x1710
> >>     btrfs_mksubvol+0xfe5/0x13f0
> >>     __btrfs_ioctl_snap_create+0x2b0/0x430
> >>     btrfs_ioctl_snap_create_v2+0x25a/0x520
> >>     btrfs_ioctl+0x2a1c/0x5ce0
> >>     __x64_sys_ioctl+0x193/0x200
> >>     do_syscall_64+0x35/0x80
> >>
> >> Fix this by introducing __update_qgroup_limit_item() helper, allocate
> >> memory outside of the spin lock.
> >>
> >> Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
> > 
> > Added to misc-next, thanks.
> 
> Please remove it for now, the patch only addressed what MM layer 
> reports, it doesn't really solve the root cause, we're doing a tree 
> modification (btrfs_search_slot()), under a spinlock.

Removed. As the potential sleeping under spinlock is hard to spot we
should add might_sleep to some places.