Messages in this thread | | | Subject | Re: [patch 2/2] Sort module list by pointer address to get coherent sleepable seq_file iterators | From | Rusty Russell <> | Date | Tue, 21 Aug 2007 10:08:29 +1000 |
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On Mon, 2007-08-20 at 16:26 -0400, Mathieu Desnoyers wrote: > plain text document attachment (module.c-sort-module-list.patch) > A race that appears both in /proc/modules and in kallsyms: if, between the > seq file reads, the process is put to sleep and at this moment a module is > or removed from the module list, the listing will skip an amount of > modules/symbols corresponding to the amount of elements present in the unloaded > module, but at the current position in the list if the iteration is located > after the removed module. > > The cleanest way I found to deal with this problem is to sort the module list. > We can then keep the old struct module * as the old iterator, knowing the it may > be removed between the seq file reads, but we only use it as "get next". If it > is not present in the module list, the next pointer will be used. > > By doing this, removing a given module will now only fuzz the output related to > this specific module, not any random module anymore. Since modprobe uses > /proc/modules, it might be important to make sure multiple concurrent running > modprobes won't interfere with each other.
You've reduced, but not eliminated, the problem. A new module inserted is quite likely to reuse the same address.
I don't have a real problem with this patch, but I'm wondering if the problem is theoretical or demonstrated.
Rusty.
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