WARNING in __alloc_skb

Status: fixed on 2023/12/11 10:30
Bug presence: origin:upstream
[Documentation on labels]
Fix commit: ab3e13b35c1a ppp: limit MRU to 64K
First crash: 164d, last: 164d
Fix bisection: fixed by (bisect log) :
commit ab3e13b35c1ada63773a276f0f8c4fec7956cb9a
Author: Willem de Bruijn <>
Date: Mon Nov 13 03:16:32 2023 +0000

  ppp: limit MRU to 64K

Bug presence (1)
Date Name Commit Repro Result
2023/11/09 upstream (ToT) 6bc986ab839c C [report] WARNING in __alloc_skb
Similar bugs (3)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING in __alloc_skb (3) ppp C 2 75d 75d 26/26 fixed on 2024/03/29 01:33
upstream WARNING in __alloc_skb arm-msm net C error 24 1138d 1150d 20/26 fixed on 2021/04/09 19:46
upstream WARNING in __alloc_skb (2) ppp C done 2 146d 160d 25/26 fixed on 2024/01/20 21:18

Sample crash report:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 11 at mm/page_alloc.c:5521 __alloc_pages+0x32c/0x730 mm/page_alloc.c:5521
Modules linked in:
CPU: 0 PID: 11 Comm: kworker/u4:1 Not tainted 6.1.62-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
Workqueue: events_unbound flush_to_ldisc
pstate: 204000c5 (nzCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : __alloc_pages+0x32c/0x730 mm/page_alloc.c:5521
lr : __alloc_pages+0xc8/0x730 mm/page_alloc.c:5515
sp : ffff800019e07740
x29: ffff800019e07820 x28: ffff800019e07760 x27: dfff800000000000
x26: ffff7000033c0eec x25: 0000000000000000 x24: ffff800019e07780
x23: 0000000000000000 x22: 0000000000060a20 x21: 1ffff000033c0ef0
x20: ffff800019e077a0 x19: 0000000000000013 x18: ffff800019e07240
x17: ffff80000d421dc4 x16: ffff800012083980 x15: ffff8000103b57c0
x14: ffff800008967774 x13: ffff80000802a900 x12: 0000000000000005
x11: 1ffff000033c0ef4 x10: 0000000000000000 x9 : 0000000000000001
x8 : ffff800018132000 x7 : 0000000000000000 x6 : 000000000000003f
x5 : 00000000ffffffff x4 : 0000000000000000 x3 : 0000000000000020
x2 : 0000000000000008 x1 : 0000000000000000 x0 : ffff800019e077a0
Call trace:
 __alloc_pages+0x32c/0x730 mm/page_alloc.c:5521
 __alloc_pages_node include/linux/gfp.h:237 [inline]
 alloc_pages_node include/linux/gfp.h:260 [inline]
 __kmalloc_large_node+0xbc/0x21c mm/slab_common.c:1096
 __do_kmalloc_node mm/slab_common.c:943 [inline]
 __kmalloc_node_track_caller+0x12c/0x1c0 mm/slab_common.c:975
 kmalloc_reserve net/core/skbuff.c:454 [inline]
 __alloc_skb+0x1b4/0x580 net/core/skbuff.c:515
 __netdev_alloc_skb+0xb8/0x3c8 net/core/skbuff.c:579
 netdev_alloc_skb include/linux/skbuff.h:3174 [inline]
 dev_alloc_skb include/linux/skbuff.h:3187 [inline]
 ppp_sync_input drivers/net/ppp/ppp_synctty.c:679 [inline]
 ppp_sync_receive+0x13c/0x7b0 drivers/net/ppp/ppp_synctty.c:342
 tty_ldisc_receive_buf+0x12c/0x15c drivers/tty/tty_buffer.c:461
 tty_port_default_receive_buf+0x74/0xac drivers/tty/tty_port.c:39
 receive_buf drivers/tty/tty_buffer.c:515 [inline]
 flush_to_ldisc+0x260/0x6f8 drivers/tty/tty_buffer.c:565
 process_one_work+0x7ac/0x1404 kernel/workqueue.c:2292
 worker_thread+0x8e4/0xfec kernel/workqueue.c:2439
 kthread+0x250/0x2d8 kernel/kthread.c:376
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:864
irq event stamp: 146750
hardirqs last  enabled at (146749): [<ffff8000122159fc>] __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:159 [inline]
hardirqs last  enabled at (146749): [<ffff8000122159fc>] _raw_spin_unlock_irq+0x3c/0x90 kernel/locking/spinlock.c:202
hardirqs last disabled at (146750): [<ffff800012215778>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (146750): [<ffff800012215778>] _raw_spin_lock_irqsave+0xa4/0xb4 kernel/locking/spinlock.c:162
softirqs last  enabled at (146742): [<ffff80000caa8cd4>] local_bh_enable+0x10/0x34 include/linux/bottom_half.h:32
softirqs last disabled at (146738): [<ffff80000caa8c1c>] local_bh_disable+0x10/0x34 include/linux/bottom_half.h:19
---[ end trace 0000000000000000 ]---
PPPsync: no memory (input pkt)
PPPsync: no memory (input pkt)

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2023/11/08 21:39 linux-6.1.y fb2635ac69ab b93f63e8 .config console log report syz C [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 WARNING in __alloc_skb
2023/11/08 21:05 linux-6.1.y fb2635ac69ab b93f63e8 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 WARNING in __alloc_skb
* Struck through repros no longer work on HEAD.