Messages in this thread | | | Subject | Re: [PATCH] EVMS core (3/9) discover.c | From | "Mark Peloquin" <> | Date | Thu, 10 Oct 2002 17:05:00 -0500 |
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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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