From: Mauro Carvalho Chehab
Sent: 30 April 2022 14:38
Em Sat, 30 Apr 2022 14:04:59 +0200 Greg KH gregkh@linuxfoundation.org escreveu:
On Sat, Apr 30, 2022 at 11:30:58AM +0100, Mauro Carvalho Chehab wrote:
Did you run checkpatch on this? Please do :)
- if (mod == this)
return 0;How can this happen? When people mistakenly call try_module_get(THIS_MODULE)?
Yes. There are lots of place where this is happening:
$ git grep try_module_get(THIS_MODULE|wc -l 82
We should throw up a big warning when that happens anyway as that's always wrong.
But that's a different issue from this change, sorry for the noise.
It sounds very weird to use try_module_get(THIS_MODULE).
We could add a WARN_ON() there - or something similar - but I would do it on a separate patch.
You could add a compile-time check. But a run-time one seems unnecessary. Clearly try_module_get(THIS_MODULE) usually succeeds.
I think I can invent a case where it can fail: The module count must be zero, and a module unload in progress. The thread doing the unload is blocked somewhere. Another thread makes a callback into the module for some request that (for instance) would need to create a kernel thread. It tries to get a reference for the thread. So try_module_get(THIS_MODULE) is the right call - and will fail here.
David
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