[syzbot] [ext4?] BUG: sleeping function called from invalid context in ext4_update_super

[syzbot] [ext4?] BUG: sleeping function called from invalid context in ext4_update_super

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f8dba31b0a82 Merge tag 'asym-keys-fix-for-linus-v6.4-rc5' ..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11b5d0dd280000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7474de833c217bf4
dashboard link: https://syzkaller.appspot.com/bug?extid=4acc7d910e617b360859
compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/92008b448c84/disk-f8dba31b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/25e27132216c/vmlinux-f8dba31b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/72466b6c1237/bzImage-f8dba31b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4acc7d910e617b360859@syzkaller.appspotmail.com

EXT4-fs error (device loop4): ext4_get_group_info:331: comm syz-executor.4: invalid group 4294819419
BUG: sleeping function called from invalid context at include/linux/buffer_head.h:404
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 21305, name: syz-executor.4
preempt_count: 1, expected: 0
RCU nest depth: 0, expected: 0
5 locks held by syz-executor.4/21305:
 #0: ffff8880292c8460 (sb_writers#4){.+.+}-{0:0}, at: do_sendfile+0x5fb/0xff0 fs/read_write.c:1253
 #1: ffff8880391da200 (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at: inode_lock include/linux/fs.h:775 [inline]
 #1: ffff8880391da200 (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at: ext4_buffered_write_iter+0xaf/0x3a0 fs/ext4/file.c:283
 #2: ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:155 [inline]
 #2: ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_convert_inline_data_to_extent fs/ext4/inline.c:584 [inline]
 #2: ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_try_to_write_inline_data+0x51d/0x1360 fs/ext4/inline.c:740
 #3: ffff8880391da088 (&ei->i_data_sem){++++}-{3:3}, at: ext4_map_blocks+0x980/0x1cf0 fs/ext4/inode.c:616
 #4: ffff88803944f018 (&bgl->locks[i].lock){+.+.}-{2:2}, at: spin_trylock include/linux/spinlock.h:360 [inline]
 #4: ffff88803944f018 (&bgl->locks[i].lock){+.+.}-{2:2}, at: ext4_lock_group fs/ext4/ext4.h:3407 [inline]
 #4: ffff88803944f018 (&bgl->locks[i].lock){+.+.}-{2:2}, at: ext4_mb_try_best_found+0x1ca/0x5a0 fs/ext4/mballoc.c:2166
Preemption disabled at:
[<0000000000000000>] 0x0
CPU: 0 PID: 21305 Comm: syz-executor.4 Not tainted 6.4.0-rc5-syzkaller-00002-gf8dba31b0a82 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/25/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
 __might_resched+0x5cf/0x780 kernel/sched/core.c:10153
 lock_buffer include/linux/buffer_head.h:404 [inline]
 ext4_update_super+0x93/0x1230 fs/ext4/super.c:6039
 ext4_commit_super+0xd0/0x4c0 fs/ext4/super.c:6117
 ext4_handle_error+0x5ee/0x8b0 fs/ext4/super.c:676
 __ext4_error+0x277/0x3b0 fs/ext4/super.c:776
 ext4_get_group_info+0x382/0x3e0 fs/ext4/balloc.c:331
 ext4_mb_new_inode_pa+0x89c/0x1300 fs/ext4/mballoc.c:4915
 ext4_mb_try_best_found+0x3a1/0x5a0 fs/ext4/mballoc.c:2171
 ext4_mb_regular_allocator+0x3511/0x3c20 fs/ext4/mballoc.c:2784
 ext4_mb_new_blocks+0xe5f/0x44a0 fs/ext4/mballoc.c:5843
 ext4_alloc_branch fs/ext4/indirect.c:340 [inline]
 ext4_ind_map_blocks+0x10d7/0x29e0 fs/ext4/indirect.c:635
 ext4_map_blocks+0x9e7/0x1cf0 fs/ext4/inode.c:625
 _ext4_get_block+0x238/0x6a0 fs/ext4/inode.c:779
 __block_write_begin_int+0x548/0x1a50 fs/buffer.c:2064
 ext4_try_to_write_inline_data+0x7ed/0x1360 fs/ext4/inline.c:740
 ext4_write_begin+0x290/0x10b0 fs/ext4/inode.c:1147
 ext4_da_write_begin+0x300/0xa40 fs/ext4/inode.c:2893
 generic_perform_write+0x300/0x5e0 mm/filemap.c:3923
 ext4_buffered_write_iter+0x122/0x3a0 fs/ext4/file.c:289
 ext4_file_write_iter+0x1d6/0x1930
 do_iter_write+0x7b1/0xcb0 fs/read_write.c:860
 iter_file_splice_write+0x843/0xfe0 fs/splice.c:795
 do_splice_from fs/splice.c:873 [inline]
 direct_splice_actor+0xe7/0x1c0 fs/splice.c:1039
 splice_direct_to_actor+0x4c4/0xbd0 fs/splice.c:994
 do_splice_direct+0x283/0x3d0 fs/splice.c:1082
 do_sendfile+0x620/0xff0 fs/read_write.c:1254
 __do_sys_sendfile64 fs/read_write.c:1322 [inline]
 __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1308
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f0ff0c8c169
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f0ff1944168 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f0ff0dabf80 RCX: 00007f0ff0c8c169
RDX: 0000000000000000 RSI: 0000000000000007 RDI: 0000000000000006
RBP: 00007f0ff0ce7ca1 R08: 0000000000000000 R09: 0000000000000000
R10: 0001000000201005 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffe35f5084f R14: 00007f0ff1944300 R15: 0000000000022000
 </TASK>
BUG: scheduling while atomic: syz-executor.4/21305/0x00000002
5 locks held by syz-executor.4/21305:
 #0: ffff8880292c8460 (sb_writers#4){.+.+}-{0:0}, at: do_sendfile+0x5fb/0xff0 fs/read_write.c:1253
 #1: ffff8880391da200 (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at: inode_lock include/linux/fs.h:775 [inline]
 #1: ffff8880391da200 (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at: ext4_buffered_write_iter+0xaf/0x3a0 fs/ext4/file.c:283
 #2: ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:155 [inline]
 #2: ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_convert_inline_data_to_extent fs/ext4/inline.c:584 [inline]
 #2: ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_try_to_write_inline_data+0x51d/0x1360 fs/ext4/inline.c:740
 #3: ffff8880391da088 (&ei->i_data_sem){++++}-{3:3}, at: ext4_map_blocks+0x980/0x1cf0 fs/ext4/inode.c:616
 #4: ffff88803944f018 (&bgl->locks[i].lock){+.+.}-{2:2}, at: spin_trylock include/linux/spinlock.h:360 [inline]
 #4: ffff88803944f018 (&bgl->locks[i].lock){+.+.}-{2:2}, at: ext4_lock_group fs/ext4/ext4.h:3407 [inline]
 #4: ffff88803944f018 (&bgl->locks[i].lock){+.+.}-{2:2}, at: ext4_mb_try_best_found+0x1ca/0x5a0 fs/ext4/mballoc.c:2166
Modules linked in:
Preemption disabled at:
[<0000000000000000>] 0x0


---
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Re: [syzbot] [ext4?] BUG: sleeping function called from invalid context in ext4_update_super

[Fabio M. De Francesco]

On sabato 10 giugno 2023 15:52:55 CEST syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f8dba31b0a82 Merge tag 'asym-keys-fix-for-linus-v6.4-rc5' ..
> git tree:       upstream
>
> [...]
> 
> Unfortunately, I don't have any reproducer for this issue yet.

Unfortunately :-(

> Downloadable assets:
>
> [...]
> 
> EXT4-fs error (device loop4): ext4_get_group_info:331: comm syz-executor.4:
> invalid group 4294819419 BUG: sleeping function called from invalid context
> at include/linux/buffer_head.h:404 in_atomic(): 1, irqs_disabled(): 0,
> non_block: 0, pid: 21305, name: syz-executor.4 preempt_count: 1, expected: 0
> RCU nest depth: 0, expected: 0
> 5 locks held by syz-executor.4/21305:
>  #0: ffff8880292c8460 (sb_writers#4){.+.+}-{0:0}, at: do_sendfile+0x5fb/
0xff0
> fs/read_write.c:1253 #1: ffff8880391da200
> (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at: inode_lock
> include/linux/fs.h:775 [inline] #1: ffff8880391da200
> (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at:
> ext4_buffered_write_iter+0xaf/0x3a0 fs/ext4/file.c:283 #2: ffff8880391d9ec8
> (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:155
> [inline] #2: ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at:
> ext4_convert_inline_data_to_extent fs/ext4/inline.c:584 [inline] #2:
> ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at:
> ext4_try_to_write_inline_data+0x51d/0x1360 fs/ext4/inline.c:740 #3:
> ffff8880391da088 (&ei->i_data_sem){++++}-{3:3}, at:
> ext4_map_blocks+0x980/0x1cf0 fs/ext4/inode.c:616 #4: ffff88803944f018
> (&bgl->locks[i].lock){+.+.}-{2:2}, at: spin_trylock
> include/linux/spinlock.h:360 [inline] #4: ffff88803944f018
> (&bgl->locks[i].lock){+.+.}-{2:2}, at: ext4_lock_group fs/ext4/ext4.h:3407
> [inline] #4: ffff88803944f018 (&bgl->locks[i].lock){+.+.}-{2:2}, at:
> ext4_mb_try_best_found+0x1ca/0x5a0 fs/ext4/mballoc.c:2166 Preemption 
disabled
> at:
> [<0000000000000000>] 0x0
> CPU: 0 PID: 21305 Comm: syz-executor.4 Not tainted
> 6.4.0-rc5-syzkaller-00002-gf8dba31b0a82 #0 Hardware name: Google Google
> Compute Engine/Google Compute Engine, BIOS Google 05/25/2023 Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
>  __might_resched+0x5cf/0x780 kernel/sched/core.c:10153
>  lock_buffer include/linux/buffer_head.h:404 [inline]
>  ext4_update_super+0x93/0x1230 fs/ext4/super.c:6039
>  ext4_commit_super+0xd0/0x4c0 fs/ext4/super.c:6117
>  ext4_handle_error+0x5ee/0x8b0 fs/ext4/super.c:676

Well, I'm a new to filesystems. However, I'd like to test a change in 
ext4_handle_error().

Currently I see that errors are handled according to the next snippet of code 
from the above-mentioned function (please note that we are in atomic context):

if (continue_fs)
	if (continue_fs && journal)
		schedule_work(&EXT4_SB(sb)->s_error_work);
	else
		ext4_commit_super(sb);

If evaluates false, we directly call ext4_commit_super(), forgetting that, 
AFAICS we are in atomic context.

Obviously, we know that ext4_update_super() calls lock_buffer(), which 
might_sleep().

As I said I have only little experience with filesystems, so my question is: 
despite the overhead, can we delete the check and do the following?

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 05fcecc36244..574b096de059 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -662,19 +662,8 @@ static void ext4_handle_error(struct super_block *sb, 
bool force_ro, int error,
                        jbd2_journal_abort(journal, -EIO);
        }
 
-       if (!bdev_read_only(sb->s_bdev)) {
-               save_error_info(sb, error, ino, block, func, line);
-               /*
-                * In case the fs should keep running, we need to writeout
-                * superblock through the journal. Due to lock ordering
-                * constraints, it may not be safe to do it right here so we
-                * defer superblock flushing to a workqueue.
-                */
-               if (continue_fs && journal)
-                       schedule_work(&EXT4_SB(sb)->s_error_work);
-               else
-                       ext4_commit_super(sb);
-       }
+       if (!bdev_read_only(sb->s_bdev))
+               schedule_work(&EXT4_SB(sb)->s_error_work);
 
        /*
         * We force ERRORS_RO behavior when system is rebooting. Otherwise we

Am I missing something I'm not able to see here?
If not, I'll try this diff if and when Syzkaller provides a reproducer.

Thanks,

Fabio

>  __ext4_error+0x277/0x3b0 fs/ext4/super.c:776
>  ext4_get_group_info+0x382/0x3e0 fs/ext4/balloc.c:331
>  ext4_mb_new_inode_pa+0x89c/0x1300 fs/ext4/mballoc.c:4915
>  ext4_mb_try_best_found+0x3a1/0x5a0 fs/ext4/mballoc.c:2171
>  ext4_mb_regular_allocator+0x3511/0x3c20 fs/ext4/mballoc.c:2784
>  ext4_mb_new_blocks+0xe5f/0x44a0 fs/ext4/mballoc.c:5843
>  ext4_alloc_branch fs/ext4/indirect.c:340 [inline]
>  ext4_ind_map_blocks+0x10d7/0x29e0 fs/ext4/indirect.c:635
>  ext4_map_blocks+0x9e7/0x1cf0 fs/ext4/inode.c:625
>  _ext4_get_block+0x238/0x6a0 fs/ext4/inode.c:779
>  __block_write_begin_int+0x548/0x1a50 fs/buffer.c:2064
>  ext4_try_to_write_inline_data+0x7ed/0x1360 fs/ext4/inline.c:740
>  ext4_write_begin+0x290/0x10b0 fs/ext4/inode.c:1147
>  ext4_da_write_begin+0x300/0xa40 fs/ext4/inode.c:2893
>  generic_perform_write+0x300/0x5e0 mm/filemap.c:3923
>  ext4_buffered_write_iter+0x122/0x3a0 fs/ext4/file.c:289
>  ext4_file_write_iter+0x1d6/0x1930
>  do_iter_write+0x7b1/0xcb0 fs/read_write.c:860
>  iter_file_splice_write+0x843/0xfe0 fs/splice.c:795
>  do_splice_from fs/splice.c:873 [inline]
>  direct_splice_actor+0xe7/0x1c0 fs/splice.c:1039
>  splice_direct_to_actor+0x4c4/0xbd0 fs/splice.c:994
>  do_splice_direct+0x283/0x3d0 fs/splice.c:1082
>  do_sendfile+0x620/0xff0 fs/read_write.c:1254
>  __do_sys_sendfile64 fs/read_write.c:1322 [inline]
>  __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1308
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f0ff0c8c169
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 00 00 90 48 89 f8 48 89 f7 
48
> 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73
> 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f0ff1944168
> EFLAGS: 00000246 ORIG_RAX: 0000000000000028 RAX: ffffffffffffffda RBX:
> 00007f0ff0dabf80 RCX: 00007f0ff0c8c169
> RDX: 0000000000000000 RSI: 0000000000000007 RDI: 0000000000000006
> RBP: 00007f0ff0ce7ca1 R08: 0000000000000000 R09: 0000000000000000
> R10: 0001000000201005 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007ffe35f5084f R14: 00007f0ff1944300 R15: 0000000000022000
>  </TASK>
> BUG: scheduling while atomic: syz-executor.4/21305/0x00000002
> 5 locks held by syz-executor.4/21305:
>  #0: ffff8880292c8460 (sb_writers#4){.+.+}-{0:0}, at: do_sendfile+0x5fb/
0xff0
> fs/read_write.c:1253 #1: ffff8880391da200
> (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at: inode_lock
> include/linux/fs.h:775 [inline] #1: ffff8880391da200
> (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at:
> ext4_buffered_write_iter+0xaf/0x3a0 fs/ext4/file.c:283 #2: ffff8880391d9ec8
> (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:155
> [inline] #2: ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at:
> ext4_convert_inline_data_to_extent fs/ext4/inline.c:584 [inline] #2:
> ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at:
> ext4_try_to_write_inline_data+0x51d/0x1360 fs/ext4/inline.c:740 #3:
> ffff8880391da088 (&ei->i_data_sem){++++}-{3:3}, at:
> ext4_map_blocks+0x980/0x1cf0 fs/ext4/inode.c:616 #4: ffff88803944f018
> (&bgl->locks[i].lock){+.+.}-{2:2}, at: spin_trylock
> include/linux/spinlock.h:360 [inline] #4: ffff88803944f018
> (&bgl->locks[i].lock){+.+.}-{2:2}, at: ext4_lock_group fs/ext4/ext4.h:3407
> [inline] #4: ffff88803944f018 (&bgl->locks[i].lock){+.+.}-{2:2}, at:
> ext4_mb_try_best_found+0x1ca/0x5a0 fs/ext4/mballoc.c:2166 Modules linked in:
> Preemption disabled at:
> [<0000000000000000>] 0x0
> 
> 
> ---

[...]

Re: [syzbot] [ext4?] BUG: sleeping function called from invalid context in ext4_update_super

[Fabio M. De Francesco]

On sabato 10 giugno 2023 22:41:18 CEST Fabio M. De Francesco wrote:
> On sabato 10 giugno 2023 15:52:55 CEST syzbot wrote:
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    f8dba31b0a82 Merge tag 'asym-keys-fix-for-linus-v6.4-rc5' 
..
> > git tree:       upstream
> > 
> > [...]
> > 
> > Unfortunately, I don't have any reproducer for this issue yet.
> 
> Unfortunately :-(
> 
> > Downloadable assets:
> > 
> > [...]
> > 
> > EXT4-fs error (device loop4): ext4_get_group_info:331: comm syz-executor.
4:
> > invalid group 4294819419 BUG: sleeping function called from invalid 
context
> > at include/linux/buffer_head.h:404 in_atomic(): 1, irqs_disabled(): 0,
> > non_block: 0, pid: 21305, name: syz-executor.4 preempt_count: 1, expected: 
0
> > RCU nest depth: 0, expected: 0
> > 
> > 5 locks held by syz-executor.4/21305:
> >  #0: ffff8880292c8460 (sb_writers#4){.+.+}-{0:0}, at: do_sendfile+0x5fb/
> 
> 0xff0
> 
> > fs/read_write.c:1253 #1: ffff8880391da200
> > (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at: inode_lock
> > include/linux/fs.h:775 [inline] #1: ffff8880391da200
> > (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at:
> > ext4_buffered_write_iter+0xaf/0x3a0 fs/ext4/file.c:283 #2: 
ffff8880391d9ec8
> > (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:
155
> > [inline] #2: ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at:
> > ext4_convert_inline_data_to_extent fs/ext4/inline.c:584 [inline] #2:
> > ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at:
> > ext4_try_to_write_inline_data+0x51d/0x1360 fs/ext4/inline.c:740 #3:
> > ffff8880391da088 (&ei->i_data_sem){++++}-{3:3}, at:
> > ext4_map_blocks+0x980/0x1cf0 fs/ext4/inode.c:616 #4: ffff88803944f018
> > (&bgl->locks[i].lock){+.+.}-{2:2}, at: spin_trylock
> > include/linux/spinlock.h:360 [inline] #4: ffff88803944f018
> > (&bgl->locks[i].lock){+.+.}-{2:2}, at: ext4_lock_group fs/ext4/ext4.h:3407
> > [inline] #4: ffff88803944f018 (&bgl->locks[i].lock){+.+.}-{2:2}, at:
> > ext4_mb_try_best_found+0x1ca/0x5a0 fs/ext4/mballoc.c:2166 Preemption
> 
> disabled
> 
> > at:
> > [<0000000000000000>] 0x0
> > CPU: 0 PID: 21305 Comm: syz-executor.4 Not tainted
> > 6.4.0-rc5-syzkaller-00002-gf8dba31b0a82 #0 Hardware name: Google Google
> > 
> > Compute Engine/Google Compute Engine, BIOS Google 05/25/2023 Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
> >  __might_resched+0x5cf/0x780 kernel/sched/core.c:10153
> >  lock_buffer include/linux/buffer_head.h:404 [inline]
> >  ext4_update_super+0x93/0x1230 fs/ext4/super.c:6039
> >  ext4_commit_super+0xd0/0x4c0 fs/ext4/super.c:6117
> >  ext4_handle_error+0x5ee/0x8b0 fs/ext4/super.c:676
> 
> Well, I'm a new to filesystems. However, I'd like to test a change in
> ext4_handle_error().
> 
> Currently I see that errors are handled according to the next snippet of 
code
> from the above-mentioned function (please note that we are in atomic 
context):
> 
> if (continue_fs)
> 	if (continue_fs && journal)
> 		schedule_work(&EXT4_SB(sb)->s_error_work);
> 	else
> 		ext4_commit_super(sb);
> 
> If evaluates false, we directly call ext4_commit_super(), forgetting that,
> AFAICS we are in atomic context.
> 
> Obviously, we know that ext4_update_super() calls lock_buffer(), which
> might_sleep().
> 
> As I said I have only little experience with filesystems, so my question is:
> despite the overhead, can we delete the check and do the following?
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 05fcecc36244..574b096de059 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -662,19 +662,8 @@ static void ext4_handle_error(struct super_block *sb,
> bool force_ro, int error,
>                         jbd2_journal_abort(journal, -EIO);
>         }
> 
> -       if (!bdev_read_only(sb->s_bdev)) {
> -               save_error_info(sb, error, ino, block, func, line);
> -               /*
> -                * In case the fs should keep running, we need to writeout
> -                * superblock through the journal. Due to lock ordering
> -                * constraints, it may not be safe to do it right here so we
> -                * defer superblock flushing to a workqueue.
> -                */
> -               if (continue_fs && journal)
> -                       schedule_work(&EXT4_SB(sb)->s_error_work);
> -               else
> -                       ext4_commit_super(sb);
> -       }
> +       if (!bdev_read_only(sb->s_bdev))
> +               schedule_work(&EXT4_SB(sb)->s_error_work);
> 
>         /*
>          * We force ERRORS_RO behavior when system is rebooting. Otherwise 
we
> 

O, sorry. I forgot something...

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 05fcecc36244..ac3a734b7d4d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -664,16 +664,7 @@ static void ext4_handle_error(struct super_block *sb, 
bool force_ro, int error,
 
        if (!bdev_read_only(sb->s_bdev)) {
                save_error_info(sb, error, ino, block, func, line);
-               /*
-                * In case the fs should keep running, we need to writeout
-                * superblock through the journal. Due to lock ordering
-                * constraints, it may not be safe to do it right here so we
-                * defer superblock flushing to a workqueue.
-                */
-               if (continue_fs && journal)
-                       schedule_work(&EXT4_SB(sb)->s_error_work);
-               else
-                       ext4_commit_super(sb);
+               schedule_work(&EXT4_SB(sb)->s_error_work);
        }
 
        /*

> Am I missing something I'm not able to see here?
> If not, I'll try this diff if and when Syzkaller provides a reproducer.
> 
> Thanks,
> 
> Fabio
> 
> >  __ext4_error+0x277/0x3b0 fs/ext4/super.c:776
> >  ext4_get_group_info+0x382/0x3e0 fs/ext4/balloc.c:331
> >  ext4_mb_new_inode_pa+0x89c/0x1300 fs/ext4/mballoc.c:4915
> >  ext4_mb_try_best_found+0x3a1/0x5a0 fs/ext4/mballoc.c:2171
> >  ext4_mb_regular_allocator+0x3511/0x3c20 fs/ext4/mballoc.c:2784
> >  ext4_mb_new_blocks+0xe5f/0x44a0 fs/ext4/mballoc.c:5843
> >  ext4_alloc_branch fs/ext4/indirect.c:340 [inline]
> >  ext4_ind_map_blocks+0x10d7/0x29e0 fs/ext4/indirect.c:635
> >  ext4_map_blocks+0x9e7/0x1cf0 fs/ext4/inode.c:625
> >  _ext4_get_block+0x238/0x6a0 fs/ext4/inode.c:779
> >  __block_write_begin_int+0x548/0x1a50 fs/buffer.c:2064
> >  ext4_try_to_write_inline_data+0x7ed/0x1360 fs/ext4/inline.c:740
> >  ext4_write_begin+0x290/0x10b0 fs/ext4/inode.c:1147
> >  ext4_da_write_begin+0x300/0xa40 fs/ext4/inode.c:2893
> >  generic_perform_write+0x300/0x5e0 mm/filemap.c:3923
> >  ext4_buffered_write_iter+0x122/0x3a0 fs/ext4/file.c:289
> >  ext4_file_write_iter+0x1d6/0x1930
> >  do_iter_write+0x7b1/0xcb0 fs/read_write.c:860
> >  iter_file_splice_write+0x843/0xfe0 fs/splice.c:795
> >  do_splice_from fs/splice.c:873 [inline]
> >  direct_splice_actor+0xe7/0x1c0 fs/splice.c:1039
> >  splice_direct_to_actor+0x4c4/0xbd0 fs/splice.c:994
> >  do_splice_direct+0x283/0x3d0 fs/splice.c:1082
> >  do_sendfile+0x620/0xff0 fs/read_write.c:1254
> >  __do_sys_sendfile64 fs/read_write.c:1322 [inline]
> >  __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1308
> >  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
> >  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > 
> > RIP: 0033:0x7f0ff0c8c169
> > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 00 00 90 48 89 f8 48 89 f7
> 
> 48
> 
> > 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 
73
> > 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f0ff1944168
> > EFLAGS: 00000246 ORIG_RAX: 0000000000000028 RAX: ffffffffffffffda RBX:
> > 00007f0ff0dabf80 RCX: 00007f0ff0c8c169
> > RDX: 0000000000000000 RSI: 0000000000000007 RDI: 0000000000000006
> > RBP: 00007f0ff0ce7ca1 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0001000000201005 R11: 0000000000000246 R12: 0000000000000000
> > R13: 00007ffe35f5084f R14: 00007f0ff1944300 R15: 0000000000022000
> > 
> >  </TASK>
> > 
> > BUG: scheduling while atomic: syz-executor.4/21305/0x00000002
> > 
> > 5 locks held by syz-executor.4/21305:
> >  #0: ffff8880292c8460 (sb_writers#4){.+.+}-{0:0}, at: do_sendfile+0x5fb/
> 
> 0xff0
> 
> > fs/read_write.c:1253 #1: ffff8880391da200
> > (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at: inode_lock
> > include/linux/fs.h:775 [inline] #1: ffff8880391da200
> > (&sb->s_type->i_mutex_key#7){++++}-{3:3}, at:
> > ext4_buffered_write_iter+0xaf/0x3a0 fs/ext4/file.c:283 #2: 
ffff8880391d9ec8
> > (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:
155
> > [inline] #2: ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at:
> > ext4_convert_inline_data_to_extent fs/ext4/inline.c:584 [inline] #2:
> > ffff8880391d9ec8 (&ei->xattr_sem){++++}-{3:3}, at:
> > ext4_try_to_write_inline_data+0x51d/0x1360 fs/ext4/inline.c:740 #3:
> > ffff8880391da088 (&ei->i_data_sem){++++}-{3:3}, at:
> > ext4_map_blocks+0x980/0x1cf0 fs/ext4/inode.c:616 #4: ffff88803944f018
> > (&bgl->locks[i].lock){+.+.}-{2:2}, at: spin_trylock
> > include/linux/spinlock.h:360 [inline] #4: ffff88803944f018
> > (&bgl->locks[i].lock){+.+.}-{2:2}, at: ext4_lock_group fs/ext4/ext4.h:3407
> > [inline] #4: ffff88803944f018 (&bgl->locks[i].lock){+.+.}-{2:2}, at:
> > ext4_mb_try_best_found+0x1ca/0x5a0 fs/ext4/mballoc.c:2166 Modules linked 
in:
> > Preemption disabled at:
> > [<0000000000000000>] 0x0
> > 
> > 
> > ---
> 
> [...]