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The source for the Linux kernel used in Windows Subsystem for Linux 2 (WSL2)
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Xianting Tian 377254b2cd fs: prevent BUG_ON in submit_bh_wbc() 
If a device is hot-removed --- for example, when a physical device is
unplugged from pcie slot or a nbd device's network is shutdown ---
this can result in a BUG_ON() crash in submit_bh_wbc().  This is
because the when the block device dies, the buffer heads will have
their Buffer_Mapped flag get cleared, leading to the crash in
submit_bh_wbc.

We had attempted to work around this problem in commit a17712c8
("ext4: check superblock mapped prior to committing").  Unfortunately,
it's still possible to hit the BUG_ON(!buffer_mapped(bh)) if the
device dies between when the work-around check in ext4_commit_super()
and when submit_bh_wbh() is finally called:

Code path:
ext4_commit_super
    judge if 'buffer_mapped(sbh)' is false, return <== commit a17712c8
          lock_buffer(sbh)
          ...
          unlock_buffer(sbh)
               __sync_dirty_buffer(sbh,...
                    lock_buffer(sbh)
                        judge if 'buffer_mapped(sbh))' is false, return <== added by this patch
                            submit_bh(...,sbh)
                                submit_bh_wbc(...,sbh,...)

[100722.966497] kernel BUG at fs/buffer.c:3095! <== BUG_ON(!buffer_mapped(bh))' in submit_bh_wbc()
[100722.966503] invalid opcode: 0000 [#1] SMP
[100722.966566] task: ffff8817e15a9e40 task.stack: ffffc90024744000
[100722.966574] RIP: 0010:submit_bh_wbc+0x180/0x190
[100722.966575] RSP: 0018:ffffc90024747a90 EFLAGS: 00010246
[100722.966576] RAX: 0000000000620005 RBX: ffff8818a80603a8 RCX: 0000000000000000
[100722.966576] RDX: ffff8818a80603a8 RSI: 0000000000020800 RDI: 0000000000000001
[100722.966577] RBP: ffffc90024747ac0 R08: 0000000000000000 R09: ffff88207f94170d
[100722.966578] R10: 00000000000437c8 R11: 0000000000000001 R12: 0000000000020800
[100722.966578] R13: 0000000000000001 R14: 000000000bf9a438 R15: ffff88195f333000
[100722.966580] FS:  00007fa2eee27700(0000) GS:ffff88203d840000(0000) knlGS:0000000000000000
[100722.966580] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[100722.966581] CR2: 0000000000f0b008 CR3: 000000201a622003 CR4: 00000000007606e0
[100722.966582] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[100722.966583] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[100722.966583] PKRU: 55555554
[100722.966583] Call Trace:
[100722.966588]  __sync_dirty_buffer+0x6e/0xd0
[100722.966614]  ext4_commit_super+0x1d8/0x290 [ext4]
[100722.966626]  __ext4_std_error+0x78/0x100 [ext4]
[100722.966635]  ? __ext4_journal_get_write_access+0xca/0x120 [ext4]
[100722.966646]  ext4_reserve_inode_write+0x58/0xb0 [ext4]
[100722.966655]  ? ext4_dirty_inode+0x48/0x70 [ext4]
[100722.966663]  ext4_mark_inode_dirty+0x53/0x1e0 [ext4]
[100722.966671]  ? __ext4_journal_start_sb+0x6d/0xf0 [ext4]
[100722.966679]  ext4_dirty_inode+0x48/0x70 [ext4]
[100722.966682]  __mark_inode_dirty+0x17f/0x350
[100722.966686]  generic_update_time+0x87/0xd0
[100722.966687]  touch_atime+0xa9/0xd0
[100722.966690]  generic_file_read_iter+0xa09/0xcd0
[100722.966694]  ? page_cache_tree_insert+0xb0/0xb0
[100722.966704]  ext4_file_read_iter+0x4a/0x100 [ext4]
[100722.966707]  ? __inode_security_revalidate+0x4f/0x60
[100722.966709]  __vfs_read+0xec/0x160
[100722.966711]  vfs_read+0x8c/0x130
[100722.966712]  SyS_pread64+0x87/0xb0
[100722.966716]  do_syscall_64+0x67/0x1b0
[100722.966719]  entry_SYSCALL64_slow_path+0x25/0x25

To address this, add the check of 'buffer_mapped(bh)' to
__sync_dirty_buffer().  This also has the benefit of fixing this for
other file systems.

With this addition, we can drop the workaround in ext4_commit_supper().

[ Commit description rewritten by tytso. ]

Signed-off-by: Xianting Tian <xianting_tian@126.com>
Link: https://lore.kernel.org/r/1596211825-8750-1-git-send-email-xianting_tian@126.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
 		2020-08-07 15:44:59 -04:00
Documentation ext4: use generic names for generic ioctls 2020-08-06 01:35:05 -04:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch x86/ldt: use "pr_info_once()" instead of open-coding it badly 2020-07-05 12:50:20 -07:00
block block-5.8-2020-07-05 2020-07-05 10:45:31 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto crypto: af_alg - fix use-after-free in af_alg_accept() due to bh_lock_sock() 2020-06-18 17:09:54 +10:00
drivers A set of interrupt chip driver fixes: 2020-07-05 12:22:35 -07:00
fs fs: prevent BUG_ON in submit_bh_wbc() 2020-08-07 15:44:59 -04:00
include ext4: add prefetch_block_bitmaps mount option 2020-08-07 14:12:35 -04:00
init kbuild: fix CONFIG_CC_CAN_LINK(_STATIC) for cross-compilation with Clang 2020-07-02 00:57:45 +09:00
ipc mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
kernel A single fix for a printk format warning in RCU. 2020-07-05 12:21:28 -07:00
lib Peter Zijlstra says: 2020-06-28 09:42:47 -07:00
mm mm/page_alloc: fix documentation error 2020-07-03 16:15:25 -07:00
net Fixes for a umask bug on exported filesystems lacking ACL support, a 2020-07-02 20:35:33 -07:00
samples samples/vfs: avoid warning in statx override 2020-07-03 16:15:25 -07:00
scripts Kbuild fixes for v5.8 (2nd) 2020-07-05 12:14:24 -07:00
security Two simple fixes for v5.8: 2020-06-30 12:21:53 -07:00
sound sound fixes for 5.8-rc3 2020-06-25 09:15:24 -07:00
tools A series of fixes for x86: 2020-07-05 12:23:49 -07:00
usr bpfilter: match bit size of bpfilter_umh to that of the kernel 2020-05-17 18:52:01 +09:00
virt MIPS: 2020-06-12 11:05:52 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: Do not track `defconfig` from `make savedefconfig` 2020-07-05 16:15:46 +09:00
.mailmap A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS mailmap: change email for Ricardo Ribalda 2020-05-25 18:59:59 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Devicetree fixes for v5.8, take 2: 2020-07-02 22:46:05 -07:00
Makefile Linux 5.8-rc4 2020-07-05 16:20:22 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.