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    SubjectRe: [ATM] first pass at fixing atm spinlock
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    In message <20030317150144.F92155@sfgoth.com>,Mitchell Blank Jr writes:
    >Note that this patch also has lots of other stuff (he driver, ipv6 stuff)

    that ipv6 stuff crept in there (due to a bad merge on my part). i believe
    i have that right now.

    >> atm_dev_lock is now a
    >> read/write lock that now protects the list of atm devices.
    >
    >Are you sure you're never sleeping while holding this lock while iterating
    >device lists? I haven't checked but we do a fair number of things there
    >(like the proc stuff) so we really need to track those down.

    fairly certain. the only dangerous thing proc.c is snprintf(). i didnt
    want to spend a lot of time on proc.c doing it the 'right' way (using
    atm_dev_hold/release) since it will be change to a seq interface.

    >sock/vcc combo can't go away while a processor's bh still is using a reference
    >to the vcc. I think this has been the result of many of the reported SMP
    >crashes (it's probably not that hard to trigger; just close an ATM socket
    >that's receiving a flood of traffic)

    i dont know. i believe all of the adapters do a synchronous close. after
    the close finishes, no more traffic should arrive for a particular vcc.
    the bottom halfs (halves?) should not have references to vcc after a close()
    for it finishes.

    >You really need something like atm_dev_release_last() that waits for the
    >reference count to hit "1" (via a completion or something) and then does
    >the release stuff.

    atm_dev_deregister() does that. if a driver need to remove the atm
    device (i suppose its being unplugged) it could close the vcc's and
    call atm_dev_register() which will wait the ref count to drop to 0.
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