I tried testing to see if this fixed [1], and it appears to be triggering a lockdep warning[2] at this line in the patch:
[1] https://syzkaller.appspot.com/bug?extid=f4582777a19ec422b517 [2] https://syzkaller.appspot.com/x/report.txt?x=17260843280000
diff --git a/fs/ext4/file.c b/fs/ext4/file.c index d101b3b0c7da..9df82d72eb90 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -808,6 +809,27 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma) if (!daxdev_mapping_supported(vma, dax_dev)) return -EOPNOTSUPP;
- /*
* Writing via mmap has no logic to handle inline data, so we* need to call ext4_convert_inline_data() to convert the inode* to normal format before doing so, otherwise a BUG_ON will be* triggered in ext4_writepages() due to the* EXT4_STATE_MAY_INLINE_DATA flag. Moreover, we need to grab* i_rwsem during conversion, since clearing and setting the* inline data flag may race with ext4_buffered_write_iter()* to trigger a BUG_ON.*/- if (ext4_has_feature_inline_data(sb) &&
vma->vm_flags & VM_SHARED && vma->vm_flags & VM_MAYWRITE) {int err;inode_lock(inode); <=================== LOCKDEP warningerr = ext4_convert_inline_data(inode);inode_unlock(inode);if (err)return err;- }
The details of the lockdep warning from [2], which appears to be a mmap(2) racing with a buffered write(2) are below. Could you take a look?
Thanks!
- Ted
====================================================== WARNING: possible circular locking dependency detected 6.4.0-rc4-syzkaller-geb1f822c76be-dirty #0 Not tainted ------------------------------------------------------ syz-executor.4/5589 is trying to acquire lock: ffff888024228168 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_lock include/linux/mmap_lock.h:142 [inline] ffff888024228168 (&mm->mmap_lock){++++}-{3:3}, at: do_user_addr_fault+0xb3d/0x1210 arch/x86/mm/fault.c:1391
but task is already holding lock: ffff88806a066800 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: inode_lock include/linux/fs.h:775 [inline] ffff88806a066800 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: ext4_buffered_write_iter+0xb0/0x460 fs/ext4/file.c:283
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&sb->s_type->i_mutex_key#8){++++}-{3:3}: down_write+0x92/0x200 kernel/locking/rwsem.c:1573 inode_lock include/linux/fs.h:775 [inline] ext4_file_mmap+0x62e/0x800 fs/ext4/file.c:826 call_mmap include/linux/fs.h:1873 [inline] mmap_region+0x694/0x28d0 mm/mmap.c:2652 do_mmap+0x831/0xf60 mm/mmap.c:1394 vm_mmap_pgoff+0x1a2/0x3b0 mm/util.c:543 ksys_mmap_pgoff+0x41f/0x5a0 mm/mmap.c:1440 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd
-> #0 (&mm->mmap_lock){++++}-{3:3}: check_prev_add kernel/locking/lockdep.c:3113 [inline] check_prevs_add kernel/locking/lockdep.c:3232 [inline] validate_chain kernel/locking/lockdep.c:3847 [inline] __lock_acquire+0x2fcd/0x5f30 kernel/locking/lockdep.c:5088 lock_acquire kernel/locking/lockdep.c:5705 [inline] lock_acquire+0x1b1/0x520 kernel/locking/lockdep.c:5670 down_read+0x9c/0x480 kernel/locking/rwsem.c:1520 mmap_read_lock include/linux/mmap_lock.h:142 [inline] do_user_addr_fault+0xb3d/0x1210 arch/x86/mm/fault.c:1391 handle_page_fault arch/x86/mm/fault.c:1534 [inline] exc_page_fault+0x98/0x170 arch/x86/mm/fault.c:1590 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570 fault_in_readable+0x1a5/0x210 mm/gup.c:1856 fault_in_iov_iter_readable+0x252/0x2c0 lib/iov_iter.c:362 generic_perform_write+0x1ae/0x570 mm/filemap.c:3913 ext4_buffered_write_iter+0x15b/0x460 fs/ext4/file.c:289 ext4_file_write_iter+0xbe0/0x1740 fs/ext4/file.c:710 call_write_iter include/linux/fs.h:1868 [inline] new_sync_write fs/read_write.c:491 [inline] vfs_write+0x945/0xd50 fs/read_write.c:584 ksys_write+0x12b/0x250 fs/read_write.c:637 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(&sb->s_type->i_mutex_key#8); lock(&mm->mmap_lock); lock(&sb->s_type->i_mutex_key#8); rlock(&mm->mmap_lock);
*** DEADLOCK ***
3 locks held by syz-executor.4/5589: #0: ffff88802a7fe0e8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe7/0x100 fs/file.c:1047 #1: ffff888021fe0460 (sb_writers#4){.+.+}-{0:0}, at: ksys_write+0x12b/0x250 fs/read_write.c:637 #2: ffff88806a066800 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: inode_lock include/linux/fs.h:775 [inline] #2: ffff88806a066800 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: ext4_buffered_write_iter+0xb0/0x460 fs/ext4/file.c:283
stack backtrace: CPU: 0 PID: 5589 Comm: syz-executor.4 Not tainted 6.4.0-rc4-syzkaller-geb1f822c76be-dirty #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+0xd9/0x150 lib/dump_stack.c:106 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2188 check_prev_add kernel/locking/lockdep.c:3113 [inline] check_prevs_add kernel/locking/lockdep.c:3232 [inline] validate_chain kernel/locking/lockdep.c:3847 [inline] __lock_acquire+0x2fcd/0x5f30 kernel/locking/lockdep.c:5088 lock_acquire kernel/locking/lockdep.c:5705 [inline] lock_acquire+0x1b1/0x520 kernel/locking/lockdep.c:5670 down_read+0x9c/0x480 kernel/locking/rwsem.c:1520 mmap_read_lock include/linux/mmap_lock.h:142 [inline] do_user_addr_fault+0xb3d/0x1210 arch/x86/mm/fault.c:1391 handle_page_fault arch/x86/mm/fault.c:1534 [inline] exc_page_fault+0x98/0x170 arch/x86/mm/fault.c:1590 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570 RIP: 0010:fault_in_readable+0x1a5/0x210 mm/gup.c:1856 Code: fc ff df 48 c7 04 02 00 00 00 00 48 83 c4 48 4c 89 e0 5b 5d 41 5c 41 5d 41 5e 41 5f c3 45 31 e4 eb ce e8 ae 51 c4 ff 45 31 f6 <41> 8a 45 00 31 ff 44 89 f6 88 44 24 28 e8 b9 4d c4 ff 45 85 f6 75 RSP: 0018:ffffc90006187a38 EFLAGS: 00050246 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffff888026905940 RSI: ffffffff81bff672 RDI: 0000000000000007 RBP: 00000000200002cc R08: 0000000000000007 R09: 0000000000000000 R10: 00000000000002c0 R11: 1ffffffff219cbe3 R12: 000000000000000c R13: 00000000200002c0 R14: 0000000000000000 R15: 1ffff92000c30f48 fault_in_iov_iter_readable+0x252/0x2c0 lib/iov_iter.c:362 generic_perform_write+0x1ae/0x570 mm/filemap.c:3913 ext4_buffered_write_iter+0x15b/0x460 fs/ext4/file.c:289 ext4_file_write_iter+0xbe0/0x1740 fs/ext4/file.c:710 call_write_iter include/linux/fs.h:1868 [inline] new_sync_write fs/read_write.c:491 [inline] vfs_write+0x945/0xd50 fs/read_write.c:584 ksys_write+0x12b/0x250 fs/read_write.c:637 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f2359a8c169 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:00007f235a721168 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f2359bac050 RCX: 00007f2359a8c169 RDX: 000000000000000c RSI: 00000000200002c0 RDI: 0000000000000004 RBP: 00007f2359ae7ca1 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ffea89659df R14: 00007f235a721300 R15: 0000000000022000 </TASK> ---------------- Code disassembly (best guess), 2 bytes skipped: 0: df 48 c7 fisttps -0x39(%rax) 3: 04 02 add $0x2,%al 5: 00 00 add %al,(%rax) 7: 00 00 add %al,(%rax) 9: 48 83 c4 48 add $0x48,%rsp d: 4c 89 e0 mov %r12,%rax 10: 5b pop %rbx 11: 5d pop %rbp 12: 41 5c pop %r12 14: 41 5d pop %r13 16: 41 5e pop %r14 18: 41 5f pop %r15 1a: c3 retq 1b: 45 31 e4 xor %r12d,%r12d 1e: eb ce jmp 0xffffffee 20: e8 ae 51 c4 ff callq 0xffc451d3 25: 45 31 f6 xor %r14d,%r14d * 28: 41 8a 45 00 mov 0x0(%r13),%al <-- trapping instruction 2c: 31 ff xor %edi,%edi 2e: 44 89 f6 mov %r14d,%esi 31: 88 44 24 28 mov %al,0x28(%rsp) 35: e8 b9 4d c4 ff callq 0xffc44df3 3a: 45 85 f6 test %r14d,%r14d 3d: 75 .byte 0x75