On 10/10/2002 at 03:48 PM, Andi Kleen wrote:
> > + list_for_each_entry(plugin, &plugin_head, headers) {
> > + if (GetPluginType(plugin->id) == EVMS_DEVICE_MANAGER) {
> > + spin_unlock(&plugin_lock);
> > + DISCOVER(plugin, disk_list);
> > + spin_lock(&plugin_lock);
> > + }
> How do you know "plugin" and its successors are still valid when retaking
> the spinlock? Looks like you need a reference count on the object here.
The spinlock itself should protect the integrity of the
list. If a prev or next element in the list should be
removed, while in a discover function, then the prev
or next field in the current plugin will get updated,
but I don't believe that should cause the list_for_each_entry
macro problems traversing the remainding elements in the list.
The first instruction in every plugin's discover function
is a MOD_INC_USE_COUNT and the last before the return is
MOD_DEC_USE_COUNT. So there exists a small window by
which the current plugin might be unloaded between the
spinlock release and MOD_INC_USE_COUNT, and the
MOD_DEC_USE_COUNT and the spinlock reacquire.
We plan to register a "__this_module.can_unload()" that
should prevent plugin modules from unloading during
discovery.
Mark
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This archive was generated by hypermail 2b29 : Tue Oct 15 2002 - 22:00:39 EST