Messages in this thread | | | Date | Fri, 31 Aug 2007 21:24:21 +0530 (IST) | From | Satyam Sharma <> | Subject | Re: [Bugme-new] [Bug 8957] New: Exported functions and variables should not be reachable by the outside of the module until module_init finishes |
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Hi Andrew,
On Wed, 29 Aug 2007, Andrew Morton wrote:
> On Wed, 29 Aug 2007 19:33:48 -0600 Robert Hancock <hancockr@shaw.ca> wrote: > > > Andrew Morton wrote: > > > On Wed, 29 Aug 2007 11:33:06 -0700 (PDT) bugme-daemon@bugzilla.kernel.org wrote: > > > > > >> http://bugzilla.kernel.org/show_bug.cgi?id=8957 > > >> > > >> Summary: Exported functions and variables should not be reachable > > >> by the outside of the module until module_init finishes > > >> Product: Other > > >> Version: 2.5 > > >> KernelVersion: 2.6.23-rc4 > > >> Platform: All > > >> OS/Version: Linux > > >> Tree: Mainline > > >> Status: NEW > > >> Severity: normal > > >> Priority: P1 > > >> Component: Modules > > >> AssignedTo: other_modules@kernel-bugs.osdl.org > > >> ReportedBy: mattilinnanvuori@yahoo.com > > >> > > >> > > >> Problem Description: a module's exported functions can be called before before > > >> they are properly initialized by the module_init function. > > >> > > >> Steps to reproduce: write a module that exports functions that require > > >> initialization by the module_init function to work correctly. > > >> > > >> E.g. spin lock variables are no longer allowed to be initialized by C > > >> initializers of the module but only by spin_lock_init that can be called by the > > >> module_init function. If an exported function calls spin_lock before it is > > >> initialized, it deadlocks. > > > > > > ooh, nice bug ;) > > > > Under what circumstances is this actually happening? What are these > > functions that are being called? > > > > Normally things are set up such that this isn't a problem, i.e. if > > module A depends on module B, module A can't load until module B is > > finished loading. > > Good point. > > This thus-far-undescribed module could make its internals externally > visible via one of the kernel's many register_foo() interfaces,
What you're saying is a plausible problem, but note that it is quite a completely different issue to what Matti Linnanvuori suggested in the original bug report.
The report was about module B (which depends on module A, because it references symbol exported by module A) being able to call a function (or access data) /exported/ by module A _without_ the module_init() function of module A having finished completely (and hence the possibility of accessing uninitialized data etc). But this is not possible -- see the last reply to Matti.
You're referring to is a module implementing an (possibly un-exported) function that refers to module-local data, and registering that function (say through a notifier_block) _before_ initializing_ the data used by that function. But ...
> but it > would be a buggy module if it was doing register_foo(my_foo) before > my_foo() was ready to be called.
... exactly. That module is the buggy culprit here, nothing wrong with the kernel's core module code.
[ BTW I suspect there /are/ modules out there that get this register_foo() ordering wrong in their module_init functions.
Even more widespread (as I have noticed) is the sad habit of modules to not unregister_foo() their stuff (in the module_exit function) in the exact reverse order of the register_foo() calls made during module_init. This can clearly lead to oopsen, but the only reason why we don't see them frequently is because the module_init and module_exit codepaths are rarely ever executed at runtime, and even more rarely concurrently with other stuff that's using the module. ]
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