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    SubjectRe: [PATCH] softirq: Use local_irq_save() in local_bh_enable()
    On Mon, Nov 17, 2008 at 03:18:28PM +0100, Johannes Berg wrote:
    > On Mon, 2008-11-17 at 13:35 +0000, Jarek Poplawski wrote:
    > > This report:
    > > shows local_bh_enable() is used in the wrong context (irqs disabled).
    > > It happens when a usual network receive path is called by netconsole,
    > > which simply turns off irqs around this all. Probably this is wrong,
    > > but it worked like this long time, and it's not trivial to fix this.
    > Unfortunately my brain lacks the magic to decrypt x86 stack traces, so
    > I'm unable to read much from that report other than that it hit the
    > WARN_ON. That looks more like the TX path to me?

    OK, this looks like both paths (which is probably common in networking).

    > Anyway, my patch made
    > that trigger for everybody rather than just on NOPREEMPT/UP (or
    > something like that) and made the code easier to understand by removing
    > the flags that are pointless anyway if the API is used correctly.
    > You can find discussion around the patch at

    Yes, it's very interesting.

    > > Anyway, a commit 0f476b6d91a1395bda6464e653ce66ea9bea7167 "softirq:
    > > remove irqs_disabled warning from local_bh_enable" can break things
    > > after changing from local_irq_save() to local_irq_disable(). Before
    > > this commit there was only a warning, now a lockup is possible, so
    > > it could be treated as a regression. This patch reverts the change
    > > in irqs.
    > Do we have evidence of this actually hitting often? This is the first
    > report of anything going wrong that I've seen ever since a single one
    > right after this commit went into testing five months ago.
    > IFF we want to add this back (and I'm not in favour) then please add a
    > big comment that this is only to accomodate broken users.

    Yes, it seems there should be more such reports from netconsole users.
    But, I guess we kind of expect this if we still use WARN_ON and not
    BUG_ON here?

    Jarek P.

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      Last update: 2008-11-18 08:53    [W:0.020 / U:9.528 seconds]
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