netdev - Suggestions on how to debug kernel crashes where printk and gdb both does not work

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Date:   Mon, 14 Jun 2021 21:22:43 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     alex.aring@...il.com, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-wpan@...r.kernel.org, netdev@...r.kernel.org,
        stefan@...enfreihafen.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        syzbot+b80c9959009a9325cdff@...kaller.appspotmail.com,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Suggestions on how to debug kernel crashes where printk and gdb both
 does not work

Dear kernel developers,

I was trying to debug the crash - memory leak in hwsim_add_one [1]
recently. However, I encountered a disgusting issue: my breakpoint and
printk/pr_alert in the functions that will be surely executed do not
work. The stack trace is in the following. I wrote this email to ask
for some suggestions on how to debug such cases?

Thanks very much. Looking forward to your reply.

[<ffffffff82b09f12>] kmalloc include/linux/slab.h:556 [inline]
[<ffffffff82b09f12>] kzalloc include/linux/slab.h:686 [inline]
[<ffffffff82b09f12>] hwsim_alloc_edge.constprop.0+0x22/0x80
drivers/net/ieee802154/mac802154_hwsim.c:385
[<ffffffff82b0b0f3>] hwsim_subscribe_all_others
drivers/net/ieee802154/mac802154_hwsim.c:709 [inline]
[<ffffffff82b0b0f3>] hwsim_add_one+0x3b3/0x640
drivers/net/ieee802154/mac802154_hwsim.c:802
[<ffffffff82b0b3c4>] hwsim_probe+0x44/0xd0
drivers/net/ieee802154/mac802154_hwsim.c:848
[<ffffffff82628bf1>] platform_probe+0x81/0x120 drivers/base/platform.c:1447
[<ffffffff82625679>] really_probe+0x159/0x500 drivers/base/dd.c:576
[<ffffffff82625aab>] driver_probe_device+0x8b/0x100 drivers/base/dd.c:763
[<ffffffff82626325>] device_driver_attach+0x105/0x110 drivers/base/dd.c:1039
[<ffffffff826263d1>] __driver_attach drivers/base/dd.c:1117 [inline]
[<ffffffff826263d1>] __driver_attach+0xa1/0x140 drivers/base/dd.c:1070
[<ffffffff82622459>] bus_for_each_dev+0xa9/0x100 drivers/base/bus.c:305
[<ffffffff826244e0>] bus_add_driver+0x160/0x280 drivers/base/bus.c:622
[<ffffffff82627233>] driver_register+0xc3/0x150 drivers/base/driver.c:171
[<ffffffff874fa3dc>] hwsim_init_module+0xae/0x107
drivers/net/ieee802154/mac802154_hwsim.c:899
[<ffffffff81001083>] do_one_initcall+0x63/0x2e0 init/main.c:1249
[<ffffffff87489873>] do_initcall_level init/main.c:1322 [inline]
[<ffffffff87489873>] do_initcalls init/main.c:1338 [inline]
[<ffffffff87489873>] do_basic_setup init/main.c:1358 [inline]
[<ffffffff87489873>] kernel_init_freeable+0x1f4/0x26e init/main.c:1560
[<ffffffff84359255>] kernel_init+0xc/0x1a7 init/main.c:1447
[<ffffffff810022ef>] ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

[1] https://groups.google.com/g/syzkaller-bugs/c/iEEZ_UOvoEY/m/6sm4bt6EAgAJ

--
My best regards to you.

     No System Is Safe!
     Dongliang Mu