From: Mauro Carvalho Chehab > Sent: 30 April 2022 14:38 > > Em Sat, 30 Apr 2022 14:04:59 +0200 > Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
