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Date:      Fri, 16 Jun 2017 07:59:31 +0000
From:      bugzilla-noreply@freebsd.org
To:        freebsd-bugs@FreeBSD.org
Subject:   [Bug 220032] [if_alc] sys/dev/alc/if_alc.c: sleep-under-mutex bugs
Message-ID:  <bug-220032-8@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D220032

            Bug ID: 220032
           Summary: [if_alc] sys/dev/alc/if_alc.c: sleep-under-mutex bugs
           Product: Base System
           Version: 11.0-RELEASE
          Hardware: i386
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs@FreeBSD.org
          Reporter: baijiaju1990@163.com

The alc driver may sleep under a mutex, and the function call paths in file
"sys/dev/alc/if_alc.c" in FreeBSD 11.0 is:
alc_resume [line 2648: acquire the mutex]
  alc_init_locked [line 2664]
    alc_init_rx_ring [line 3911]
      alc_newbuf [line 4469]
        bus_dmamap_load_mbuf_sg(BUS_DMA_WAITOK) [line 3472] --> may sleep

alc_int_task [line 3330: acquire the mutex]
  alc_start_locked [line 3372]
    alc_encap [line 2942]
      bus_dmamap_load_mbuf_sg(BUS_DMA_WAITOK) [line 2780] --> may sleep

The possible fix of these bugs is to set the last parameter in
bus_dmamap_load_mbuf_sg to "BUS_DMA_NOWAIT".

This bug is found by a static analysis tool written by myself, and it is
checked by my review of the FreeBSD code.

By the way, I am a freshman in developing FreeBSD drivers, and I am willing=
 to
submit a patch. But I do not know how to write and submit a patch, and wher=
e to
submit, so I am looking forward to useful advice :)

Jia-Ju Bai

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