linux-kernel - Re: [PATCH] sparc/pci: Make pci_poke_lock a raw_spinlock

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Message-ID: <c77c77d4-7f6e-450c-97d5-39dc50d81b1a@roeck-us.net>
Date: Mon, 25 Nov 2024 09:59:09 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
 Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>,
 Waiman Long <longman@...hat.com>, Will Deacon <will@...nel.org>,
 "David S. Miller" <davem@...emloft.net>,
 Andreas Larsson <andreas@...sler.com>
Subject: Re: [PATCH] sparc/pci: Make pci_poke_lock a raw_spinlock_t.

On 11/25/24 09:43, Sebastian Andrzej Siewior wrote:
> On 2024-11-25 09:01:33 [-0800], Guenter Roeck wrote:
>> Unfortunately it doesn't make a difference.
> 
> stunning. It looks like the exact same error message.
> 

I think it uses

#define spin_lock_irqsave(lock, flags)                          \
do {                                                            \
         raw_spin_lock_irqsave(spinlock_check(lock), flags);     \
} while (0)

from include/linux/spinlock.h, meaning your patch doesn't really make a difference.

>> [    1.050499] =============================
>> [    1.050801] [ BUG: Invalid wait context ]
>> [    1.051200] 6.12.0+ #1 Not tainted
>> [    1.051571] -----------------------------
>> [    1.051875] swapper/0/1 is trying to lock:
>> [    1.052201] 0000000001b694c8 (pci_poke_lock){....}-{3:3}, at: pci_config_read16+0x8/0x80
>> [    1.052994] other info that might help us debug this:
>> [    1.053331] context-{5:5}
>> [    1.053641] 2 locks held by swapper/0/1:
>> [    1.053959]  #0: fffff800042b50f8 (&dev->mutex){....}-{4:4}, at: __driver_attach+0x80/0x160
>> [    1.054388]  #1: 0000000001d29078 (pci_lock){....}-{2:2}, at: pci_bus_read_config_word+0x18/0x80
>> [    1.054793] stack backtrace:
>> [    1.055171] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.12.0+ #1
>> [    1.055632] Call Trace:
>> [    1.055985] [<00000000004e31d0>] __lock_acquire+0xa50/0x3160
>> [    1.056329] [<00000000004e63e8>] lock_acquire+0xe8/0x340
>> [    1.056645] [<00000000010f0dfc>] _raw_spin_lock_irqsave+0x3c/0x80
>> [    1.056966] [<0000000000443828>] pci_config_read16+0x8/0x80
>> [    1.057278] [<000000000044442c>] sun4u_read_pci_cfg+0x12c/0x1a0
>> [    1.057593] [<0000000000b7657c>] pci_bus_read_config_word+0x3c/0x80
>> [    1.057913] [<0000000000b7fa78>] pci_find_capability+0x18/0xa0
>> [    1.058228] [<0000000000b794b0>] set_pcie_port_type+0x10/0x160
>> [    1.058543] [<0000000000442a98>] pci_of_scan_bus+0x158/0xb00
>> [    1.058854] [<00000000010c74a0>] pci_scan_one_pbm+0xd0/0xf8
>> [    1.059167] [<0000000000446174>] sabre_probe+0x1f4/0x5c0
>> [    1.059476] [<0000000000c13a48>] platform_probe+0x28/0x80
>> [    1.059785] [<0000000000c11158>] really_probe+0xb8/0x340
>> [    1.060098] [<0000000000c11584>] driver_probe_device+0x24/0xe0
>> [    1.060413] [<0000000000c117ac>] __driver_attach+0x8c/0x160
>> [    1.060728] [<0000000000c0ef54>] bus_for_each_dev+0x54/0xc0
>>
>> The original call trace also included _raw_spin_lock_irqsave(), and
>> I don't have CONFIG_PREEMPT_RT enabled in my sparc64 builds to start with.
> 
> You don't have to. "CONFIG_PROVE_RAW_LOCK_NESTING" looks if you try to
> acquire raw_spinlock_t -> spinlock_t. Which it did before I made the
> patch.
> The pci_lock is from drivers/pci/access.c and is defined as
> raw_spinlock_t. And I made pci_poke_lock of the same time. But debug
> says 3:3 which suggests LD_WAIT_CONFIG. (No patch applied).
> 
>> FWIW, I don't understand the value of
>> 	pr_warn("context-{%d:%d}\n", curr_inner, curr_inner);
>> Why print curr_inner twice ?
> 
> The syntax was once (or is) inner:outer. If you look from the top, you
> have 4 (mutex_t) followed pci_lock (the raw_spinlock_t) 2. You are at
> level 2 now and try to acquire spin_lock_t (3).
> 

How does that explain the
	context-{5:5}
which is created from the following ?
	pr_warn("context-{%d:%d}\n", curr_inner, curr_inner);

Again, why print curr_inner twice ?

Thanks,
Guenter