David S. Miller wrote:
On Mon, 18 Apr 2005 14:37:22 -0700
Ben Greear <greearb@xxxxxxxxxxxxxxx> wrote:
So, two questions:
1) Why is it bad to have interrupts disabled when calling
the local_bh_enable() method?
Because it creates a deadlock. You can always take hard IRQ disabling
locks inside of BH disabling ones, but _never_ the other way around.
local_bh_enable() potentially runs BH handlers, and this must occur with
hard IRQs enabled.
Ok. It would be great if this explanation was in comments near the warning
in the code.
The dev_start_xmit code in dev.c could also have a note mentioning that it
must never be called with IRQs disabled.
2) Should there be a hard requirement that one must never have IRQs disabled
when calling dev->hard_start_xmit (this requirement seems to currently
be in effect because VLANs can call dev_queue_xmit from their
hard_start_xmit
method, and it appears that dev_queue_xmit must not be called with IRQs
disabled).
Yes, it is another true requirement.
This would be a good addition to the Documentation/networking/netdevices.txt
file, or maybe to the dev.c file somewhere (I haven't found an complete list of
locking notes, though the comments in the dev.c file and the netdevices.txt file
are a big help.)
I should be able to fix my particular problem by using reference counting and
breaking up my big loop into smaller work units.
I assume that it is fine to nest calls to local_bh_enable/disable? (This
seems to be required since you are supposed to have bh disabled when
calling hard_start_xmit, but hard_start_xmit can call dev_queue_xmit which
disables the bh again...)
Thanks,
Ben
--
Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc http://www.candelatech.com
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