module: wait when loading a module which is currently initializing.
The original module-init-tools module loader used a fnctl lock on the .ko file to avoid attempts to simultaneously load a module. Unfortunately, you can't get an exclusive fcntl lock on a read-only fd, making this not work for read-only mounted filesystems. module-init-tools has a hacky sleep-and-loop for this now. It's not that hard to wait in the kernel, and only return -EEXIST once the first module has finished loading (or continue loading the module if the first one failed to initialize for some reason). It's also consistent with what we do for dependent modules which are still loading. Suggested-by: Lucas De Marchi <firstname.lastname@example.org> Signed-off-by: Rusty Russell <email@example.com>
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