Re: [syzbot] [mm?] INFO: rcu detected stall in seq_read_iter (2)

[syzbot <syzbot+c4cf28ed38d86d6b549d@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: rcu detected stall in corrupted

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	(detected by 0, t=10502 jiffies, g=13101, q=1926589 ncpus=2)
rcu: All QSes seen, last rcu_preempt kthread activity 10500 (4294975059-4294964559), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10501 jiffies! g13101 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:25296 pid:17    tgid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5322 [inline]
 __schedule+0x1843/0x4ae0 kernel/sched/core.c:6682
 __schedule_loop kernel/sched/core.c:6759 [inline]
 schedule+0x14b/0x320 kernel/sched/core.c:6774
 schedule_timeout+0x1be/0x310 kernel/time/timer.c:2615
 rcu_gp_fqs_loop+0x2df/0x1330 kernel/rcu/tree.c:2045
 rcu_gp_kthread+0xa7/0x3b0 kernel/rcu/tree.c:2247
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 UID: 0 PID: 16 Comm: ksoftirqd/0 Not tainted 6.12.0-rc3-syzkaller-gc964ced77262-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
RIP: 0010:ip_output+0xcd/0x230 net/ipv4/ip_output.c:429
Code: 00 00 e8 46 44 7b f7 42 80 3c 33 00 74 08 4c 89 e7 e8 07 d4 e1 f7 49 8b 1c 24 48 83 e3 fe 48 89 d8 48 c1 e8 03 42 80 3c 30 00 <74> 08 48 89 df e8 e9 d3 e1 f7 4c 8b 23 4d 8d 7d 10 4c 89 fd 48 c1
RSP: 0018:ffffc90000156da8 EFLAGS: 00000246
RAX: 1ffff11030ec32e0 RBX: ffff888187619700 RCX: ffff88801beeda00
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff888187619700 R08: ffffffff8a19a267 R09: 1ffffffff2037a45
R10: dffffc0000000000 R11: fffffbfff2037a46 R12: ffff888187618b98
R13: ffff888187618b40 R14: dffffc0000000000 R15: ffff888187618b40
FS:  0000000000000000(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa227d5f5b0 CR3: 000000000e734000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 </IRQ>
 <TASK>
 synproxy_send_client_synack+0x8b8/0xf30 net/netfilter/nf_synproxy_core.c:484
 nft_synproxy_eval_v4+0x3ca/0x610 net/netfilter/nft_synproxy.c:59
 nft_synproxy_do_eval+0x362/0xa60 net/netfilter/nft_synproxy.c:141
 expr_call_ops_eval net/netfilter/nf_tables_core.c:240 [inline]
 nft_do_chain+0x4ad/0x1da0 net/netfilter/nf_tables_core.c:288
 nft_do_chain_inet+0x418/0x6b0 net/netfilter/nft_chain_filter.c:161
 nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
 nf_hook_slow+0xc3/0x220 net/netfilter/core.c:626
 nf_hook include/linux/netfilter.h:269 [inline]
 NF_HOOK+0x29e/0x450 include/linux/netfilter.h:312
 NF_HOOK+0x3a4/0x450 include/linux/netfilter.h:314
 __netif_receive_skb_one_core net/core/dev.c:5666 [inline]
 __netif_receive_skb+0x2bf/0x650 net/core/dev.c:5779
 process_backlog+0x662/0x15b0 net/core/dev.c:6111
 __napi_poll+0xcb/0x490 net/core/dev.c:6775
 napi_poll net/core/dev.c:6844 [inline]
 net_rx_action+0x89b/0x1240 net/core/dev.c:6966
 handle_softirqs+0x2c5/0x980 kernel/softirq.c:554
 run_ksoftirqd+0xca/0x130 kernel/softirq.c:927
 smpboot_thread_fn+0x544/0xa30 kernel/smpboot.c:164
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>


Tested on:

commit:         c964ced7 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16e90240580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=164d2822debd8b0d
dashboard link: https://syzkaller.appspot.com/bug?extid=c4cf28ed38d86d6b549d
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=14ccf887980000