linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference at 00000000000001e0

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Message-ID: <49489eb2-c7f5-369b-4552-d888cbc27719@suse.cz>
Date:   Mon, 24 Oct 2016 17:28:24 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Borislav Petkov <bp@...en8.de>, linux-serial@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Michael Galbraith <mgalbraith@...e.de>
Subject: Re: BUG: unable to handle kernel NULL pointer dereference at
 00000000000001e0

On 10/24/2016, 04:48 PM, Borislav Petkov wrote:
> Hi people,
> 
> typing "reboot" splats the following on the serial console. Ideas?
> 
> INIT: Sending p[  427.863916] BUG: unable to handle kernel NULL pointer dereference at 00000000000001e0
> [  427.885156] IP: [<ffffffffa24bfb6c>] tty_wakeup+0xc/0x70
> [  427.898337] PGD 0 [  427.902051] 
> [  427.907498] Oops: 0000 [#1] PREEMPT SMP
> [  427.917635] Modules linked in: nfsv3 nfs_acl nfs fscache lockd sunrpc grace edd af_packet cpufreq_conservative cpufreq_userspace cpufreq_powersave fuse loop md_mod dm_mod joydev hid_generic usbhid ipmi_ssif ohci_pci ohci_hcd ehci_pci ehci_hcd e1000e ptp firewire_ohci edac_core pps_core tpm_infineon sp5100_tco firewire_core acpi_cpufreq serio_raw pcspkr fjes usbcore shpchp edac_mce_amd tpm_tis ipmi_si tpm_tis_core i2c_piix4 k10temp sg ipmi_msghandler tpm sr_mod button cdrom kvm_amd kvm irqbypass crc_itu_t ast ttm drm_kms_helper drm fb_sys_fops sysimgblt sysfillrect syscopyarea i2c_algo_bit scsi_dh_rdac scsi_dh_alua scsi_dh_emc scsi_dh_hp_sw ata_generic pata_atiixp
> [  428.054179] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.9.0-rc1-1.g73e3f23-default #1
> [  428.072868] Hardware name: System manufacturer System Product Name/KGP(M)E-D16, BIOS 0902    12/03/2010
> [  428.094755] task: ffffffffa2c0d500 task.stack: ffffffffa2c00000
> [  428.109717] RIP: 0010:[<ffffffffa24bfb6c>]  [<ffffffffa24bfb6c>] tty_wakeup+0xc/0x70
> [  428.128407] RSP: 0018:ffff9a1a5fc03df8  EFLAGS: 00010086
> [  428.142184] RAX: ffff9a1857258000 RBX: ffffffffa3050ea0 RCX: 0000000000000000
> [  428.159649] RDX: 000000000000001b RSI: 0000000000000000 RDI: 0000000000000000
> [  428.177109] RBP: ffff9a1a5fc03e08 R08: 0000000000000000 R09: 0000000000000000
> [  428.194547] R10: 0000000000021c77 R11: 0000000000000000 R12: ffff9a1857258000
> [  428.212002] R13: 0000000000000000 R14: 0000000000000020 R15: 0000000000000020
> [  428.229481] FS:  0000000000000000(0000) GS:ffff9a1a5fc00000(0000) knlGS:0000000000000000
> [  428.248938] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  428.263726] CR2: 00000000000001e0 CR3: 0000000390c06000 CR4: 00000000000006f0
> [  428.281331] Stack:
> [  428.288696]  ffffffffa3050ea0 ffff9a1857258000 ffff9a1a5fc03e18 ffffffffa24e0ab1
> [  428.307064]  ffff9a1a5fc03e40 ffffffffa24e8865 ffffffffa3050ea0 00000000000000c2
> [  428.325456]  0000000000000046 ffff9a1a5fc03e78 ffffffffa24e8a5f ffffffffa3050ea0
> [  428.343905] Call Trace:
> [  428.352319]  <IRQ> [  428.356216]  [<ffffffffa24e0ab1>] uart_write_wakeup+0x21/0x30

>From the quick look, uart_write_wakeup should now be using refcounting.
Does this help (compile-tested only)?

--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -106,12 +106,17 @@ static inline struct uart_port
*uart_port_check(struct uart_state *state)
 void uart_write_wakeup(struct uart_port *port)
 {
        struct uart_state *state = port->state;
+       struct tty_struct *ttyp;
        /*
         * This means you called this function _after_ the port was
         * closed.  No cookie for you.
         */
        BUG_ON(!state);
-       tty_wakeup(state->port.tty);
+
+       ttyp = tty_port_tty_get(&state->port);
+       if (ttyp)
+               tty_wakeup(ttyp);
+       tty_kref_put(ttyp);
 }

 static void uart_stop(struct tty_struct *tty)


thanks,
-- 
js
suse labs