Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 3 Jul 2023 10:07:28 -0700 | Subject | Re: [mm] 408579cd62: WARNING:suspicious_RCU_usage |
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On Mon, 3 Jul 2023 at 10:00, Conor Dooley <conor@kernel.org> wrote: > > I'm not entirely sure if it is related, as stuff in the guts of mm like > this is beyond me, but I've been seeing similar warnings on RISC-V.
No, that RISC-V warning is also about bad RCU usage, but that's a different thing.
> RCU used illegally from offline CPU! > rcu_scheduler_active = 1, debug_locks = 1 > 1 lock held by swapper/1/0: > #0: ffffffff8169ceb0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x32 > > stack backtrace: > CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.4.0-10173-ga901a3568fd2 #1 > Hardware name: riscv-virtio,qemu (DT) > Call Trace: > [<ffffffff80006a20>] show_stack+0x2c/0x38 > [<ffffffff80af3ee0>] dump_stack_lvl+0x5e/0x80 > [<ffffffff80af3f16>] dump_stack+0x14/0x1c > [<ffffffff80083ff0>] lockdep_rcu_suspicious+0x19e/0x232 > [<ffffffff80ad4802>] mtree_load+0x18a/0x3b6 > [<ffffffff80091632>] __irq_get_desc_lock+0x2c/0x82 > [<ffffffff80094722>] enable_percpu_irq+0x36/0x9e > [<ffffffff800087d4>] riscv_ipi_enable+0x32/0x4e > [<ffffffff80008692>] smp_callin+0x24/0x66
This is also triggering on the maple tree sanity checks, but it' sa different maple tree, and a different code sequence.
And a different case of suspicious RCU usage - not a lack of locking, but simply using RCU before marking the CPU online.
I suspect the riscv_ipi_enable() in the RISC-V version of smp_callin() needs to be moved down to below the
set_cpu_online(curr_cpuid, 1);
or was there some reason why it needed to be done quite _that_ early in commit 832f15f42646 ("RISC-V: Treat IPIs as normal Linux IRQs")?
Added guilty parties to the cc.
Linus
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