linux-kernel - [PATCH 3.16 53/61] ext4: add cond_resched() to ext4_protect_reserved

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Message-ID: <lsq.1591725832.257400743@decadent.org.uk>
Date:   Tue, 09 Jun 2020 19:04:44 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        stable@...nel.org, "Theodore Ts'o" <tytso@....edu>,
        "Jan Kara" <jack@...e.cz>, "Shijie Luo" <luoshijie1@...wei.com>
Subject: [PATCH 3.16 53/61] ext4: add cond_resched() to ext4_protect_reserved_inode

3.16.85-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Shijie Luo <luoshijie1@...wei.com>

commit af133ade9a40794a37104ecbcc2827c0ea373a3c upstream.

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]

Link: https://lore.kernel.org/r/20200211011752.29242-1-luoshijie1@huawei.com
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Shijie Luo <luoshijie1@...wei.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Cc: stable@...nel.org
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext4/block_validity.c | 1 +
 1 file changed, 1 insertion(+)

--- a/fs/ext4/block_validity.c
+++ b/fs/ext4/block_validity.c
@@ -153,6 +153,7 @@ static int ext4_protect_reserved_inode(s
 		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);