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From:   Zheyu Ma <zheyuma97@gmail.com>
To:     scott@spiteful.org, bhelgaas@google.com
Cc:     linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        Zheyu Ma <zheyuma97@gmail.com>
Subject: [PATCH] PCI: hotplug: set 'thread_finished' flag to be true by default
Date:   Thu, 10 Jun 2021 03:02:41 +0000
Message-Id: <1623294161-7917-1-git-send-email-zheyuma97@gmail.com>
Precedence: bulk

In the process of probing the driver 'cpcihp_zt5550', function
'pci_get_device' may fail, at this time 'cpci_hp_unregister_controller'
will be called. Since the default value of 'thread_finished' is 0,
'cpci_stop_thread' will be executed, but at this time 'cpci_thread' has
not been allocated, which leads to a null pointer dereference.

Fix this by set 'thread_finished' to be true by default.

This log reveals it:

BUG: kernel NULL pointer dereference, address: 0000000000000028
PGD 0 P4D 0
Oops: 0002 [#1] PREEMPT SMP PTI
CPU: 5 PID: 1 Comm: swapper/0 Not tainted 5.12.4-g70e7f0549188-dirty #74
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
RIP: 0010:kthread_stop+0x51/0x380
Code: b5 4e 10 00 65 8b 05 46 da e1 7e 89 c0 48 0f a3 05 5c c1 ef 05 0f 82 68 01 00 00 e8 99 4e 10 00 4c 8d 6b 28 41 bc 01 00 00 00 <f0> 44 0f c1 63 28 45 85 e4 0f 84 af 02 00 00 e8 7b 4e 10 00 45 85
RSP: 0000:ffffc90000017ba8 EFLAGS: 00010293
RAX: ffff888100850000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff811f3b37 RDI: ffffffff86259ca6
RBP: ffffc90000017bc8 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000001 R11: 00000000ffffffff R12: 0000000000000001
R13: 0000000000000028 R14: ffff88810160a0c8 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff88817b200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000028 CR3: 0000000006a32000 CR4: 00000000000006e0
Call Trace:
 cpci_stop_thread+0x1a/0x30
 cpci_hp_unregister_controller+0x43/0xc0
 zt5550_hc_init_one+0x67d/0x720
 local_pci_probe+0x4f/0xb0
 pci_device_probe+0x169/0x230
 ? pci_device_remove+0x110/0x110
 really_probe+0x283/0x650
 driver_probe_device+0x89/0x1d0
 ? mutex_lock_nested+0x1b/0x20
 device_driver_attach+0x68/0x70
 __driver_attach+0x11c/0x1b0
 ? device_driver_attach+0x70/0x70
 bus_for_each_dev+0xbb/0x110
 ? rdinit_setup+0x45/0x45
 driver_attach+0x27/0x30
 bus_add_driver+0x1eb/0x2a0
 driver_register+0xa9/0x180
 __pci_register_driver+0x7c/0x90
 ? cpci_hotplug_init+0x1c/0x1c
 zt5550_init+0x66/0x91
 do_one_initcall+0x7f/0x3d0
 ? rdinit_setup+0x45/0x45
 ? rcu_read_lock_sched_held+0x4f/0x80
 kernel_init_freeable+0x2d7/0x329
 ? rest_init+0x2c0/0x2c0
 kernel_init+0x18/0x190
 ? rest_init+0x2c0/0x2c0
 ? rest_init+0x2c0/0x2c0
 ret_from_fork+0x1f/0x30
Modules linked in:
Dumping ftrace buffer:
   (ftrace buffer empty)
CR2: 0000000000000028
---[ end trace ef108f49fd26a20c ]---
RIP: 0010:kthread_stop+0x51/0x380
Code: b5 4e 10 00 65 8b 05 46 da e1 7e 89 c0 48 0f a3 05 5c c1 ef 05 0f 82 68 01 00 00 e8 99 4e 10 00 4c 8d 6b 28 41 bc 01 00 00 00 <f0> 44 0f c1 63 28 45 85 e4 0f 84 af 02 00 00 e8 7b 4e 10 00 45 85
RSP: 0000:ffffc90000017ba8 EFLAGS: 00010293
RAX: ffff888100850000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff811f3b37 RDI: ffffffff86259ca6
RBP: ffffc90000017bc8 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000001 R11: 00000000ffffffff R12: 0000000000000001
R13: 0000000000000028 R14: ffff88810160a0c8 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff88817b200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000028 CR3: 0000000006a32000 CR4: 00000000000006e0
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 1 seconds..

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 drivers/pci/hotplug/cpci_hotplug_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/hotplug/cpci_hotplug_core.c b/drivers/pci/hotplug/cpci_hotplug_core.c
index d0559d2faf50..d527aae4cc60 100644
--- a/drivers/pci/hotplug/cpci_hotplug_core.c
+++ b/drivers/pci/hotplug/cpci_hotplug_core.c
@@ -47,7 +47,7 @@ static atomic_t extracting;
 int cpci_debug;
 static struct cpci_hp_controller *controller;
 static struct task_struct *cpci_thread;
-static int thread_finished;
+static int thread_finished = 1;
 
 static int enable_slot(struct hotplug_slot *slot);
 static int disable_slot(struct hotplug_slot *slot);
-- 
2.17.6