Re: [syzbot] [mm?] BUG: sleeping function called from invalid context in vma_alloc_folio_noprof (2)

[Hillf Danton <hdanton@sina.com>]

> Date: Sun, 03 May 2026 04:47:26 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    dca922e019dd Merge tag 'xsa48x-7.1-tag' of git://git.kerne..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=100242ce580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d0f0911eedbc130a
> dashboard link: https://syzkaller.appspot.com/bug?extid=a21650c1666eae7b2aae
> compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> userspace arch: i386
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-dca922e0.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/1e719cb224ff/vmlinux-dca922e0.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/79a541b03a9e/bzImage-dca922e0.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a21650c1666eae7b2aae@syzkaller.appspotmail.com
> 
> BUG: sleeping function called from invalid context at ./include/linux/sched/mm.h:323
> in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 5665, name: dhcpcd-run-hook
> preempt_count: 0, expected: 0
> RCU nest depth: 1, expected: 0
> 2 locks held by dhcpcd-run-hook/5665:
>  #0: ffff8880243d01c8 (vm_lock){++++}-{0:0}, at: lock_vma_under_rcu+0x11d/0x590 mm/mmap_lock.c:310
>  #1: ffffffff8e7e52e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
>  #1: ffffffff8e7e52e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
>  #1: ffffffff8e7e52e0 (rcu_read_lock){....}-{1:3}, at: __pte_offset_map+0x2f/0x310 mm/pgtable-generic.c:290
> CPU: 0 UID: 0 PID: 5665 Comm: dhcpcd-run-hook Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
>  __might_resched.cold+0x1ec/0x232 kernel/sched/core.c:9162
>  might_alloc include/linux/sched/mm.h:323 [inline]
>  prepare_alloc_pages+0x44a/0x5f0 mm/page_alloc.c:4995
>  __alloc_frozen_pages_noprof+0x19a/0x2bc0 mm/page_alloc.c:5215
>  alloc_pages_mpol+0x1fb/0x540 mm/mempolicy.c:2490
>  folio_alloc_mpol_noprof+0x36/0x260 mm/mempolicy.c:2509
>  vma_alloc_folio_noprof+0xed/0x1d0 mm/mempolicy.c:2544
>  folio_prealloc mm/memory.c:1193 [inline]
>  wp_page_copy mm/memory.c:3859 [inline]
>  do_wp_page+0x1ee1/0x4350 mm/memory.c:4320

Given pte_unmap_unlock() [1] before wp_page_copy(), the lockdep record
of rcu lock above looks false positive. Baffled.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/memory.c#n4315

>  handle_pte_fault mm/memory.c:6427 [inline]
>  __handle_mm_fault+0x1ab6/0x2a00 mm/memory.c:6549
>  handle_mm_fault+0x36d/0xa20 mm/memory.c:6718
>  do_user_addr_fault+0x5a3/0x12f0 arch/x86/mm/fault.c:1334
>  handle_page_fault arch/x86/mm/fault.c:1474 [inline]
>  exc_page_fault+0x6f/0xd0 arch/x86/mm/fault.c:1527
>  asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
> RIP: 0033:0x7f5a6f60980e
> Code: df e8 d7 c4 ff ff 48 8d 3d 9c 92 05 00 31 c0 e8 e1 ca ff ff 95 75 24 48 8d 05 5e 9c 07 00 44 89 f2 4c 89 e6 48 89 df 48 8b 00 <83> a0 f8 02 00 00 00 e8 de eb ff ff e9 a8 00 00 00 48 85 db 0f 84
> RSP: 002b:00007ffc0b5c63f0 EFLAGS: 00010246
> RAX: 000055c4ea134910 RBX: 000055c4ea135c60 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 000055c4ea138c30 RDI: 000055c4ea135c60
> RBP: 0000000000000000 R08: 00007f5a6f5b4b60 R09: 0000000000000000
> R10: 0000000000000008 R11: 0000000000000246 R12: 000055c4ea138c30
> R13: 000055c4ea135c60 R14: 0000000000000000 R15: 0000000000000000
>  </TASK>
> 
> ================================================
> WARNING: lock held when returning to user space!
> syzkaller #0 Tainted: G        W          
> ------------------------------------------------
> dhcpcd-run-hook/5665 is leaving the kernel with locks still held!
> 1 lock held by dhcpcd-run-hook/5665:
>  #0: ffffffff8e7e52e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
>  #0: ffffffff8e7e52e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
>  #0: ffffffff8e7e52e0 (rcu_read_lock){....}-{1:3}, at: __pte_offset_map+0x2f/0x310 mm/pgtable-generic.c:290
> 
> 
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