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Date:   Mon, 10 Feb 2020 11:21:46 +0100
From:   Jan Kara <jack@suse.cz>
To:     Shijie Luo <luoshijie1@huawei.com>
Cc:     linux-ext4@vger.kernel.org, tytso@mit.edu, jack@suse.cz,
        zhangyi@huawei.com
Subject: Re: [PATCH] ext4: add cond_resched() to ext4_protect_reserved_inode
Message-ID: <20200210102146.GD12923@quack2.suse.cz>
References: <20200207062716.3068-1-luoshijie1@huawei.com>
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On Fri 07-02-20 01:27:16, Shijie Luo wrote:
> When journal size is set too big by "mkfs.ext4 -J size=", or when
> we mount a crafted image to make journal inode->i_size too big,
> the loop, "while (i < num)", holds cpu too long. This could cause
> soft lockup.
> 
> [  529.357541] Call trace:
> [  529.357551]  dump_backtrace+0x0/0x198
> [  529.357555]  show_stack+0x24/0x30
> [  529.357562]  dump_stack+0xa4/0xcc
> [  529.357568]  watchdog_timer_fn+0x300/0x3e8
> [  529.357574]  __hrtimer_run_queues+0x114/0x358
> [  529.357576]  hrtimer_interrupt+0x104/0x2d8
> [  529.357580]  arch_timer_handler_virt+0x38/0x58
> [  529.357584]  handle_percpu_devid_irq+0x90/0x248
> [  529.357588]  generic_handle_irq+0x34/0x50
> [  529.357590]  __handle_domain_irq+0x68/0xc0
> [  529.357593]  gic_handle_irq+0x6c/0x150
> [  529.357595]  el1_irq+0xb8/0x140
> [  529.357599]  __ll_sc_atomic_add_return_acquire+0x14/0x20
> [  529.357668]  ext4_map_blocks+0x64/0x5c0 [ext4]
> [  529.357693]  ext4_setup_system_zone+0x330/0x458 [ext4]
> [  529.357717]  ext4_fill_super+0x2170/0x2ba8 [ext4]
> [  529.357722]  mount_bdev+0x1a8/0x1e8
> [  529.357746]  ext4_mount+0x44/0x58 [ext4]
> [  529.357748]  mount_fs+0x50/0x170
> [  529.357752]  vfs_kern_mount.part.9+0x54/0x188
> [  529.357755]  do_mount+0x5ac/0xd78
> [  529.357758]  ksys_mount+0x9c/0x118
> [  529.357760]  __arm64_sys_mount+0x28/0x38
> [  529.357764]  el0_svc_common+0x78/0x130
> [  529.357766]  el0_svc_handler+0x38/0x78
> [  529.357769]  el0_svc+0x8/0xc
> [  541.356516] watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [mount:18674]
> 
> Signed-off-by: Shijie Luo <luoshijie1@huawei.com>

Thanks for the patch. It looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/ext4/block_validity.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
> index 1ee04e76bbe0..0a734ffb4310 100644
> --- a/fs/ext4/block_validity.c
> +++ b/fs/ext4/block_validity.c
> @@ -207,6 +207,7 @@ static int ext4_protect_reserved_inode(struct super_block *sb,
>  		return PTR_ERR(inode);
>  	num = (inode->i_size + sb->s_blocksize - 1) >> sb->s_blocksize_bits;
>  	while (i < num) {
> +		cond_resched();
>  		map.m_lblk = i;
>  		map.m_len = num - i;
>  		n = ext4_map_blocks(NULL, inode, &map, 0);
> -- 
> 2.19.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR