Re: [PATCH Resend 4.4] MIPS: Use async IPIs for arch_trigger_cpumask_backtrace()

[Greg KH <greg@kroah.com>]

On Tue, Jul 17, 2018 at 04:17:11PM +0800, Huacai Chen wrote:
> From: Paul Burton <paul.burton@mips.com>
> 
> The current MIPS implementation of arch_trigger_cpumask_backtrace() is
> broken because it attempts to use synchronous IPIs despite the fact that
> it may be run with interrupts disabled.
> 
> This means that when arch_trigger_cpumask_backtrace() is invoked, for
> example by the RCU CPU stall watchdog, we may:
> 
>   - Deadlock due to use of synchronous IPIs with interrupts disabled,
>     causing the CPU that's attempting to generate the backtrace output
>     to hang itself.
> 
>   - Not succeed in generating the desired output from remote CPUs.
> 
>   - Produce warnings about this from smp_call_function_many(), for
>     example:
> 
>     [42760.526910] INFO: rcu_sched detected stalls on CPUs/tasks:
>     [42760.535755]  0-...!: (1 GPs behind) idle=ade/140000000000000/0 softirq=526944/526945 fqs=0
>     [42760.547874]  1-...!: (0 ticks this GP) idle=e4a/140000000000000/0 softirq=547885/547885 fqs=0
>     [42760.559869]  (detected by 2, t=2162 jiffies, g=266689, c=266688, q=33)
>     [42760.568927] ------------[ cut here ]------------
>     [42760.576146] WARNING: CPU: 2 PID: 1216 at kernel/smp.c:416 smp_call_function_many+0x88/0x20c
>     [42760.587839] Modules linked in:
>     [42760.593152] CPU: 2 PID: 1216 Comm: sh Not tainted 4.15.4-00373-gee058bb4d0c2 #2
>     [42760.603767] Stack : 8e09bd20 8e09bd20 8e09bd20 fffffff0 00000007 00000006 00000000 8e09bca8
>     [42760.616937]         95b2b379 95b2b379 807a0080 00000007 81944518 0000018a 00000032 00000000
>     [42760.630095]         00000000 00000030 80000000 00000000 806eca74 00000009 8017e2b8 000001a0
>     [42760.643169]         00000000 00000002 00000000 8e09baa4 00000008 808b8008 86d69080 8e09bca0
>     [42760.656282]         8e09ad50 805e20aa 00000000 00000000 00000000 8017e2b8 00000009 801070ca
>     [42760.669424]         ...
>     [42760.673919] Call Trace:
>     [42760.678672] [<27fde568>] show_stack+0x70/0xf0
>     [42760.685417] [<84751641>] dump_stack+0xaa/0xd0
>     [42760.692188] [<699d671c>] __warn+0x80/0x92
>     [42760.698549] [<68915d41>] warn_slowpath_null+0x28/0x36
>     [42760.705912] [<f7c76c1c>] smp_call_function_many+0x88/0x20c
>     [42760.713696] [<6bbdfc2a>] arch_trigger_cpumask_backtrace+0x30/0x4a
>     [42760.722216] [<f845bd33>] rcu_dump_cpu_stacks+0x6a/0x98
>     [42760.729580] [<796e7629>] rcu_check_callbacks+0x672/0x6ac
>     [42760.737476] [<059b3b43>] update_process_times+0x18/0x34
>     [42760.744981] [<6eb94941>] tick_sched_handle.isra.5+0x26/0x38
>     [42760.752793] [<478d3d70>] tick_sched_timer+0x1c/0x50
>     [42760.759882] [<e56ea39f>] __hrtimer_run_queues+0xc6/0x226
>     [42760.767418] [<e88bbcae>] hrtimer_interrupt+0x88/0x19a
>     [42760.775031] [<6765a19e>] gic_compare_interrupt+0x2e/0x3a
>     [42760.782761] [<0558bf5f>] handle_percpu_devid_irq+0x78/0x168
>     [42760.790795] [<90c11ba2>] generic_handle_irq+0x1e/0x2c
>     [42760.798117] [<1b6d462c>] gic_handle_local_int+0x38/0x86
>     [42760.805545] [<b2ada1c7>] gic_irq_dispatch+0xa/0x14
>     [42760.812534] [<90c11ba2>] generic_handle_irq+0x1e/0x2c
>     [42760.820086] [<c7521934>] do_IRQ+0x16/0x20
>     [42760.826274] [<9aef3ce6>] plat_irq_dispatch+0x62/0x94
>     [42760.833458] [<6a94b53c>] except_vec_vi_end+0x70/0x78
>     [42760.840655] [<22284043>] smp_call_function_many+0x1ba/0x20c
>     [42760.848501] [<54022b58>] smp_call_function+0x1e/0x2c
>     [42760.855693] [<ab9fc705>] flush_tlb_mm+0x2a/0x98
>     [42760.862730] [<0844cdd0>] tlb_flush_mmu+0x1c/0x44
>     [42760.869628] [<cb259b74>] arch_tlb_finish_mmu+0x26/0x3e
>     [42760.877021] [<1aeaaf74>] tlb_finish_mmu+0x18/0x66
>     [42760.883907] [<b3fce717>] exit_mmap+0x76/0xea
>     [42760.890428] [<c4c8a2f6>] mmput+0x80/0x11a
>     [42760.896632] [<a41a08f4>] do_exit+0x1f4/0x80c
>     [42760.903158] [<ee01cef6>] do_group_exit+0x20/0x7e
>     [42760.909990] [<13fa8d54>] __wake_up_parent+0x0/0x1e
>     [42760.917045] [<46cf89d0>] smp_call_function_many+0x1a2/0x20c
>     [42760.924893] [<8c21a93b>] syscall_common+0x14/0x1c
>     [42760.931765] ---[ end trace 02aa09da9dc52a60 ]---
>     [42760.938342] ------------[ cut here ]------------
>     [42760.945311] WARNING: CPU: 2 PID: 1216 at kernel/smp.c:291 smp_call_function_single+0xee/0xf8
>     ...
> 
> This patch switches MIPS' arch_trigger_cpumask_backtrace() to use async
> IPIs & smp_call_function_single_async() in order to resolve this
> problem. We ensure use of the pre-allocated call_single_data_t
> structures is serialized by maintaining a cpumask indicating that
> they're busy, and refusing to attempt to send an IPI when a CPU's bit is
> set in this mask. This should only happen if a CPU hasn't responded to a
> previous backtrace IPI - ie. if it's hung - and we print a warning to
> the console in this case.
> 
> I've marked this for stable branches as far back as v4.9, to which it
> applies cleanly. Strictly speaking the faulty MIPS implementation can be
> traced further back to commit 856839b76836 ("MIPS: Add
> arch_trigger_all_cpu_backtrace() function") in v3.19, but kernel
> versions v3.19 through v4.8 will require further work to backport due to
> the rework performed in commit 9a01c3ed5cdb ("nmi_backtrace: add more
> trigger_*_cpu_backtrace() methods").
> 
> Signed-off-by: Paul Burton <paul.burton@mips.com>
> Patchwork: https://patchwork.linux-mips.org/patch/19597/
> Cc: James Hogan <jhogan@kernel.org>
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: linux-mips@linux-mips.org
> Cc: stable@vger.kernel.org
> Fixes: 856839b76836 ("MIPS: Add arch_trigger_all_cpu_backtrace() function")
> Fixes: 9a01c3ed5cdb ("nmi_backtrace: add more trigger_*_cpu_backtrace() methods")
> [ Huacai: backported to 4.4: Restruction since generic NMI solution is unavailable ]
> Signed-off-by: Huacai Chen <chenhc@lemote.com>
> ---
>  arch/mips/kernel/process.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)

Always give me a hint as to what the original git commit id is in
Linus's tree please.

Also, this patch does not apply at all to the 4.4.y tree :(

greg k-h