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Re: Memory barrier needed with wake_up_process()?

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: Memory barrier needed with wake_up_process()?
Date 2016-09-06 17:10 +0200
Message-ID <seqaC-3Da-35@gated-at.bofh.it> (permalink)
References <senFM-1Z9-13@gated-at.bofh.it> <sepRg-3ha-39@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Tue, Sep 06, 2016 at 10:46:55AM -0400, Alan Stern wrote:

Not knowing where INFO() goes, you should use trace_printk() not
printk(), as the former is strictly per cpu, while the latter is
globally serialized and can hide all these problems.

> Index: usb-4.x/drivers/usb/gadget/function/f_mass_storage.c
> ===================================================================
> --- usb-4.x.orig/drivers/usb/gadget/function/f_mass_storage.c
> +++ usb-4.x/drivers/usb/gadget/function/f_mass_storage.c
> @@ -485,6 +485,8 @@ static void bulk_out_complete(struct usb
>  	spin_lock(&common->lock);
>  	bh->outreq_busy = 0;
>  	bh->state = BUF_STATE_FULL;
> +	if (bh->bulk_out_intended_length == US_BULK_CB_WRAP_LEN)
> +		INFO(common, "compl: bh %p state %d\n", bh, bh->state);
>  	wakeup_thread(common);
>  	spin_unlock(&common->lock);
>  }
> @@ -2207,6 +2209,7 @@ static int get_next_command(struct fsg_c
>  		rc = sleep_thread(common, true);
>  		if (rc)
>  			return rc;
> +		INFO(common, "next: bh %p state %d\n", bh, bh->state);
>  	}
>  	smp_rmb();
>  	rc = fsg_is_set(common) ? received_cbw(common->fsg, bh) : -EIO;
>

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Thread

Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-02 20:20 +0200
  Re: Memory barrier needed with wake_up_process()? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-02 20:50 +0200
    Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-02 22:30 +0200
      Re: Memory barrier needed with wake_up_process()? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-03 11:10 +0200
      Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-03 14:40 +0200
        Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-03 16:30 +0200
          Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-03 16:50 +0200
            Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-05 10:40 +0200
              Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-05 17:30 +0200
                Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-06 13:40 +0200
                Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-06 13:50 +0200
                Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-06 14:30 +0200
                Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-06 16:50 +0200
                Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-06 17:10 +0200
                Re: Memory barrier needed with wake_up_process()? Felipe Balbi <felipe.balbi@linux.intel.com> - 2016-09-07 12:20 +0200
                Re: Memory barrier needed with wake_up_process()? Felipe Balbi <felipe.balbi@linux.intel.com> - 2016-09-06 13:50 +0200
  Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-02 21:30 +0200
    Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-02 22:20 +0200
      Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-03 00:20 +0200
        Re: Memory barrier needed with wake_up_process()? Will Deacon <will.deacon@arm.com> - 2016-09-05 11:50 +0200
          Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-06 13:20 +0200
      Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-03 00:20 +0200
        Re: Memory barrier needed with wake_up_process()? Felipe Balbi <felipe.balbi@linux.intel.com> - 2016-09-03 09:00 +0200
          Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-03 14:50 +0200
            Re: Memory barrier needed with wake_up_process()? Felipe Balbi <felipe.balbi@linux.intel.com> - 2016-09-03 16:00 +0200
              Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-05 10:10 +0200
            Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-03 16:20 +0200
              Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-05 10:10 +0200
                Re: Memory barrier needed with wake_up_process()? Alan Stern <stern@rowland.harvard.edu> - 2016-09-05 16:40 +0200
      Re: Memory barrier needed with wake_up_process()? Peter Zijlstra <peterz@infradead.org> - 2016-09-03 00:20 +0200

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