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Message-ID: <aNvh2Cd2i9MVA1d3@mozart.vkv.me>
Date: Tue, 30 Sep 2025 06:57:44 -0700
From: Calvin Owens <calvin@...nvd.org>
To: Breno Leitao <leitao@...ian.org>
Cc: Petr Mladek <pmladek@...e.com>, John Ogness <john.ogness@...utronix.de>,
Mike Galbraith <efault@....de>, Simon Horman <horms@...nel.org>,
kuba@...nel.org, Pavel Begunkov <asml.silence@...il.com>,
Johannes Berg <johannes@...solutions.net>, paulmck@...nel.org,
LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org,
boqun.feng@...il.com, Sergey Senozhatsky <senozhatsky@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>
Subject: Re: netconsole: HARDIRQ-safe -> HARDIRQ-unsafe lock order warning
On Wednesday 09/10 at 11:26 -0700, Breno Leitao wrote:
> On Wed, Sep 10, 2025 at 05:12:43PM +0200, Petr Mladek wrote:
> > On Wed 2025-09-10 14:28:40, John Ogness wrote:
>
> > > @pmladek: We could introduce a new console flag (NBCON_ATOMIC_UNSAFE) so
> > > that the callback is only used by nbcon_atomic_flush_unsafe().
> >
> > This might be an acceptable compromise. It would try to emit messages
> > only at the very end of panic() as the last desperate attempt.
> >
> > Just to be sure, what do you mean with unsafe?
> >
> > + taking IRQ unsafe locks?
>
> Taking IRQ unsafe locks is the major issue we have in netconsole today.
> Basically the drivers can implement IRQ unsafe locks in their
> .ndo_start_xmit() callback, and in some cases those are IRQ unsafe,
> which doesn't match with .write_atomic(), which expect all the inner
> locks to be IRQ safe.
Hmm, I'm also hitting the below on next-20250926 with translated=strict,
the triggering acquisition is here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/iommu/iova.c?id=30d4efb2f5a515a60fe6b0ca85362cbebea21e2f#n832
Naively I'd think the IOMMU code would need to be safe to call with
interrupts disabled? Do we need raw_spin_lock() in some places there?
I'll have more time to dig and maybe send a patch tomorrow, any quick
thoughts are appreciated.
[ 319.006534][ T16] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
[ 319.006536][ T16] in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 16, name: pr/legacy
[ 319.006537][ T16] preempt_count: 0, expected: 0
[ 319.006537][ T16] RCU nest depth: 3, expected: 3
[ 319.006538][ T16] 8 locks held by pr/legacy/16:
[ 319.006539][ T16] #0: ffffffff831ffbe0 (console_lock){+.+.}-{0:0}, at: legacy_kthread_func+0x1e/0xc0
[ 319.006546][ T16] #1: ffffffff831ffc30 (console_srcu){....}-{0:0}, at: console_flush_all+0xf2/0x430
[ 319.006550][ T16] #2: ffffffff832c3ef8 (target_list_lock){+.+.}-{3:3}, at: write_ext_msg.part.0+0x28/0x4d0
[ 319.006554][ T16] #3: ffffffff83202720 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0xd5/0x1a0
[ 319.006557][ T16] #4: ffffffff83202720 (rcu_read_lock){....}-{1:3}, at: __netpoll_send_skb+0x4a/0x3c0
[ 319.006561][ T16] #5: ffff888107c89e98 (_xmit_ETHER#2){+...}-{3:3}, at: __netpoll_send_skb+0x2d6/0x3c0
[ 319.006564][ T16] #6: ffffffff83202720 (rcu_read_lock){....}-{1:3}, at: rt_spin_trylock+0x59/0x130
[ 319.006567][ T16] #7: ffffe8ffffc06218 (&cpu_rcache->lock){+.+.}-{3:3}, at: alloc_iova_fast+0x70/0x2d0
[ 319.006570][ T16] irq event stamp: 20680
[ 319.006571][ T16] hardirqs last enabled at (20679): [<ffffffff81ee7c3c>] _raw_spin_unlock_irqrestore+0x3c/0x50
[ 319.006573][ T16] hardirqs last disabled at (20680): [<ffffffff81d37b40>] netpoll_send_skb+0x30/0x70
[ 319.006575][ T16] softirqs last enabled at (0): [<ffffffff8138970a>] copy_process+0x7aa/0x1940
[ 319.006577][ T16] softirqs last disabled at (0): [<0000000000000000>] 0x0
[ 319.006580][ T16] CPU: 0 UID: 0 PID: 16 Comm: pr/legacy Not tainted 6.17.0-rc7-next-20250926 #1 PREEMPT_{RT,LAZY}
[ 319.006582][ T16] Hardware name: ASUSTeK COMPUTER INC. WS C246M PRO Series/WS C246M PRO Series, BIOS 3301 03/23/2020
[ 319.006583][ T16] Call Trace:
[ 319.006584][ T16] <TASK>
[ 319.006586][ T16] dump_stack_lvl+0x57/0x80
[ 319.006590][ T16] __might_resched.cold+0xec/0xfd
[ 319.006592][ T16] rt_spin_lock+0x52/0x1a0
[ 319.006594][ T16] ? alloc_iova_fast+0x70/0x2d0
[ 319.006598][ T16] alloc_iova_fast+0x70/0x2d0
[ 319.006603][ T16] iommu_dma_alloc_iova+0xca/0x100
[ 319.006606][ T16] __iommu_dma_map+0x7f/0x170
[ 319.006611][ T16] iommu_dma_map_phys+0xb7/0x190
[ 319.006615][ T16] dma_map_phys+0xc9/0x130
[ 319.006619][ T16] igc_tx_map.isra.0+0x155/0x570
[ 319.006625][ T16] igc_xmit_frame_ring+0x2f3/0x510
[ 319.006627][ T16] ? rt_spin_trylock+0x59/0x130
[ 319.006631][ T16] netpoll_start_xmit+0x11c/0x190
[ 319.006635][ T16] __netpoll_send_skb+0x32b/0x3c0
[ 319.006640][ T16] netpoll_send_skb+0x3e/0x70
[ 319.006643][ T16] write_ext_msg.part.0+0x457/0x4d0
[ 319.006650][ T16] console_emit_next_record+0xcb/0x1c0
[ 319.006656][ T16] console_flush_all+0x274/0x430
[ 319.006660][ T16] ? devkmsg_write+0x110/0x110
[ 319.006663][ T16] __console_flush_and_unlock+0x34/0xa0
[ 319.006666][ T16] legacy_kthread_func+0x23/0xc0
[ 319.006669][ T16] ? swake_up_locked+0x50/0x50
[ 319.006672][ T16] kthread+0xf9/0x200
[ 319.006675][ T16] ? kthread_fetch_affinity.isra.0+0x40/0x40
[ 319.006678][ T16] ret_from_fork+0xff/0x150
[ 319.006681][ T16] ? kthread_fetch_affinity.isra.0+0x40/0x40
[ 319.006682][ T16] ? kthread_fetch_affinity.isra.0+0x40/0x40
[ 319.006684][ T16] ret_from_fork_asm+0x11/0x20
[ 319.006694][ T16] </TASK>
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