• Kosuke Tatsukawa's avatar
    brcmfmac: fix waitqueue_active without memory barrier in brcmfmac driver · a7decc44
    Kosuke Tatsukawa authored
    brcmf_msgbuf_ioctl_resp_wake() seems to be missing a memory barrier
    which might cause the waker to not notice the waiter and miss sending a
    wake_up as in the following figure.
    
      brcmf_msgbuf_ioctl_resp_wake		    brcmf_msgbuf_ioctl_resp_wait
    ------------------------------------------------------------------------
    if (waitqueue_active(&msgbuf->ioctl_resp_wait))
    /* The CPU might reorder the test for
       the waitqueue up here, before
       prior writes complete */
       	   	     	 	       /* wait_event_timeout */
    				        /* __wait_event_timeout */
    					 /* ___wait_event */
    					 prepare_to_wait_event(&wq, &__wait,
    					   state);
    					 if (msgbuf->ctl_completed)
    					 ...
    msgbuf->ctl_completed = true;
    					 schedule_timeout(__ret))
    ------------------------------------------------------------------------
    
    There are three other place in drivers/net/wireless/brcm80211/brcmfmac/
    which have similar code.  The attached patch removes the call to
    waitqueue_active() leaving just wake_up() behind.  This fixes the
    problem because the call to spin_lock_irqsave() in wake_up() will be an
    ACQUIRE operation.
    
    I found this issue when I was looking through the linux source code
    for places calling waitqueue_active() before wake_up*(), but without
    preceding memory barriers, after sending a patch to fix a similar
    issue in drivers/tty/n_tty.c  (Details about the original issue can be
    found here: https://lkml.org/lkml/2015/9/28/849).
    Reviewed-by: default avatarHante Meuleman <meuleman@broadcom.com>
    Reviewed-by: default avatarFranky (Zhenhui) Lin <frankyl@broadcom.com>
    Reviewed-by: default avatarPieter-Paul Giesberts <pieterpg@broadcom.com>
    Signed-off-by: default avatarKosuke Tatsukawa <tatsu@ab.jp.nec.com>
    Signed-off-by: default avatarArend van Spriel <arend@broadcom.com>
    Signed-off-by: default avatarKalle Valo <kvalo@codeaurora.org>
    a7decc44
usb.c 36.7 KB