On Tue, 15 Dec 2020 18:15:06 -0800 Wei Wang wrote:
On Tue, Dec 15, 2020 at 5:53 PM Jakub Kicinski [off-list ref] wrote:
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On Tue, 15 Dec 2020 17:25:14 -0800 Wei Wang wrote:
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+void napi_enable(struct napi_struct *n)
+{
+ bool locked = rtnl_is_locked();
Maybe you'll prove me wrong but I think this is never a correct
construct.
Sorry, I don't get what you mean here.
You're checking if the mutex is locked, not if the caller is holding
the mutex.
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+ BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state));
+ smp_mb__before_atomic();
+ clear_bit(NAPI_STATE_SCHED, &n->state);
+ clear_bit(NAPI_STATE_NPSVC, &n->state);
+ if (!locked)
+ rtnl_lock();
Why do we need the lock? Can't we assume the caller of napi_enable()
has the sole ownership of the napi instance? Surely clearing the other
flags would be pretty broken as well, so the napi must had been
disabled when this is called by the driver.
Hmm... OK. The reason I added this lock operation is that we have
ASSERT_RTNL() check in napi_set_threaded(), because it is necessary
from the net-sysfs path to grab rtnl lock when modifying the threaded
mode. Maybe it is not needed here.
Fair point, the sysfs write path could try to change the setting while
the NIC is starting.
And the reason I added a rtnl_is_locked() check is I found mlx driver
already holds rtnl lock before calling napi_enable(). Not sure about
other drivers though.
I'd think most drivers will only mess around with napi under rtnl_lock.
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+ WARN_ON(napi_set_threaded(n, n->dev->threaded));
+ if (!locked)
+ rtnl_unlock();
+}
+EXPORT_SYMBOL(napi_enable);