Re: [PATCH] ttyprintk: fix a potential sleeping in interrupt context issue

[Greg KH]

On Wed, Dec 11, 2019 at 09:11:46PM +0800, Zhenzhong Duan wrote:
> Google syzbot reports:
> BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:938
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/1
> 1 lock held by swapper/1/0:
> ...
> Call Trace:
>   <IRQ>
>   dump_stack+0x197/0x210
>   ___might_sleep.cold+0x1fb/0x23e
>   __might_sleep+0x95/0x190
>   __mutex_lock+0xc5/0x13c0
>   mutex_lock_nested+0x16/0x20
>   tpk_write+0x5d/0x340
>   resync_tnc+0x1b6/0x320
>   call_timer_fn+0x1ac/0x780
>   run_timer_softirq+0x6c3/0x1790
>   __do_softirq+0x262/0x98c
>   irq_exit+0x19b/0x1e0
>   smp_apic_timer_interrupt+0x1a3/0x610
>   apic_timer_interrupt+0xf/0x20
>   </IRQ>
> 
> This patch fix it by using spinlock in process context instead of
> mutex and having interrupt disabled in critical section.
> 
> Reported-by: syzbot+2eeef62ee31f9460ad65@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
> ---
>  drivers/char/ttyprintk.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/char/ttyprintk.c b/drivers/char/ttyprintk.c
> index 4f24e46ebe7c..56db949a7b70 100644
> --- a/drivers/char/ttyprintk.c
> +++ b/drivers/char/ttyprintk.c
> @@ -15,10 +15,11 @@
>  #include <linux/serial.h>
>  #include <linux/tty.h>
>  #include <linux/module.h>
> +#include <linux/spinlock.h>
> 
>  struct ttyprintk_port {
>   struct tty_port port;
> - struct mutex port_write_mutex;
> + spinlock_t spinlock;
>  };
> 
>  static struct ttyprintk_port tpk_port;
> @@ -99,11 +100,12 @@ static int tpk_open(struct tty_struct *tty,
> struct file *filp)
>  static void tpk_close(struct tty_struct *tty, struct file *filp)
>  {
>   struct ttyprintk_port *tpkp = tty->driver_data;
> + unsigned long flags;
> 
> - mutex_lock(&tpkp->port_write_mutex);
> + spin_lock_irqsave(&tpkp->spinlock, flags);
>   /* flush tpk_printk buffer */
>   tpk_printk(NULL, 0);
> - mutex_unlock(&tpkp->port_write_mutex);
> + spin_unlock_irqrestore(&tpkp->spinlock, flags);
> 
>   tty_port_close(&tpkp->port, tty, filp);
>  }


Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

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thanks,

greg k-h's patch email bot