[syzbot ci] Re: f2fs: enable buffered RWF_DONTCACHE

[syzbot ci <syzbot+cid5582b8164122eda@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v4] f2fs: enable buffered RWF_DONTCACHE
https://lore.kernel.org/all/cover.1788438786.git.qiwenjie@xiaomi.com
* [PATCH v4 1/2] f2fs: complete dropbehind write bios in task context
* [PATCH v4 2/2] f2fs: enable buffered RWF_DONTCACHE

and found the following issue:
general protection fault in f2fs_write_begin

Full report is available here:
https://ci.syzbot.org/series/cbb9ded8-1388-4a7b-bfa7-44082b04025b

***

general protection fault in f2fs_write_begin

tree:      mm-new
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git
base:      e3fc12b08aadde9cec7b3799ac0e0c9a1aa245c4
arch:      amd64
compiler:  Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
config:    https://ci.syzbot.org/builds/e5903709-6ea2-4b1e-9dfc-f073e36367f7/config
syz repro: https://ci.syzbot.org/findings/d05a5d64-e9a3-4714-9b41-43042eaaa82c/syz_repro

loop0: detected capacity change from 0 to 40427
F2FS-fs (loop0): invalid crc value
F2FS-fs (loop0): f2fs_recover_fsync_data: recovery fsync data, check_only: 0
F2FS-fs (loop0): Mounted with checkpoint version = 48b305e5
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000004: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
CPU: 1 UID: 0 PID: 5791 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:f2fs_write_begin+0x181/0x28e0 fs/f2fs/data.c:3893
Code: e7 e8 23 21 d4 fd 49 8b 04 24 48 89 44 24 40 41 c6 45 2c 04 c7 84 24 a0 02 00 00 00 00 00 00 48 83 c3 20 48 89 d8 48 c1 e8 03 <42> 0f b6 04 30 84 c0 0f 85 e9 23 00 00 41 be 80 00 00 00 44 23 33
RSP: 0018:ffffc900037af7a0 EFLAGS: 00010202
RAX: 0000000000000004 RBX: 0000000000000020 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: ffff8881b465c918 RDI: 0000000000000000
RBP: ffffc900037afad0 R08: ffffc900037afb80 R09: ffffc900037afba0
R10: dffffc0000000000 R11: ffffffff8463a450 R12: ffff88816b91e678
R13: fffff520006f5f1c R14: dffffc0000000000 R15: ffff8881b465c918
FS:  00007f65b5e096c0(0000) GS:ffff8882a8cd9000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f65b4e70050 CR3: 000000016a860000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 page_symlink+0x27a/0x440 fs/namei.c:6556
 f2fs_symlink+0x5fc/0x970 fs/f2fs/namei.c:714
 vfs_symlink+0x18b/0x330 fs/namei.c:5794
 filename_symlinkat+0x1cd/0x410 fs/namei.c:5819
 __do_sys_symlinkat fs/namei.c:5839 [inline]
 __se_sys_symlinkat+0x4e/0x2b0 fs/namei.c:5834
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f65b4f9e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f65b5e09028 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 00007f65b5225fa0 RCX: 00007f65b4f9e159
RDX: 00002000000005c0 RSI: ffffffffffffff9c RDI: 0000200000000700
RBP: 00007f65b5035024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f65b5226038 R14: 00007f65b5225fa0 R15: 00007fffb6ecc0c8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:f2fs_write_begin+0x181/0x28e0 fs/f2fs/data.c:3893
Code: e7 e8 23 21 d4 fd 49 8b 04 24 48 89 44 24 40 41 c6 45 2c 04 c7 84 24 a0 02 00 00 00 00 00 00 48 83 c3 20 48 89 d8 48 c1 e8 03 <42> 0f b6 04 30 84 c0 0f 85 e9 23 00 00 41 be 80 00 00 00 44 23 33
RSP: 0018:ffffc900037af7a0 EFLAGS: 00010202
RAX: 0000000000000004 RBX: 0000000000000020 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: ffff8881b465c918 RDI: 0000000000000000
RBP: ffffc900037afad0 R08: ffffc900037afb80 R09: ffffc900037afba0
R10: dffffc0000000000 R11: ffffffff8463a450 R12: ffff88816b91e678
R13: fffff520006f5f1c R14: dffffc0000000000 R15: ffff8881b465c918
FS:  00007f65b5e096c0(0000) GS:ffff8882a8cd9000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f65b4feb840 CR3: 000000016a860000 CR4: 00000000000006f0
----------------
Code disassembly (best guess), 1 bytes skipped:
   0:	e8 23 21 d4 fd       	call   0xfdd42128
   5:	49 8b 04 24          	mov    (%r12),%rax
   9:	48 89 44 24 40       	mov    %rax,0x40(%rsp)
   e:	41 c6 45 2c 04       	movb   $0x4,0x2c(%r13)
  13:	c7 84 24 a0 02 00 00 	movl   $0x0,0x2a0(%rsp)
  1a:	00 00 00 00
  1e:	48 83 c3 20          	add    $0x20,%rbx
  22:	48 89 d8             	mov    %rbx,%rax
  25:	48 c1 e8 03          	shr    $0x3,%rax
* 29:	42 0f b6 04 30       	movzbl (%rax,%r14,1),%eax <-- trapping instruction
  2e:	84 c0                	test   %al,%al
  30:	0f 85 e9 23 00 00    	jne    0x241f
  36:	41 be 80 00 00 00    	mov    $0x80,%r14d
  3c:	44 23 33             	and    (%rbx),%r14d


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
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Notes:
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