Messages in this thread | | | Date | Mon, 3 Jul 2023 18:20:52 +0100 | From | Conor Dooley <> | Subject | Re: [mm] 408579cd62: WARNING:suspicious_RCU_usage |
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On Mon, Jul 03, 2023 at 10:07:28AM -0700, Linus Torvalds wrote: > 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.
Ah, I probably should've known from the RCU used illegally from offline CPU! that it was different.
> 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.
Taking the rationale & potential problems out of the equation, that code movement does suppress the complaints from rcu/maple tree, thanks.
Cheers, Conor. [unhandled content-type:application/pgp-signature] | |