On Mon, May 2, 2016 at 5:13 PM, Chen Gang <chengang@xxxxxxxxxxxxxxxx> wrote: > On 5/2/16 22:23, Alexander Potapenko wrote: >> On Mon, May 2, 2016 at 3:51 PM, Chen Gang <chengang@xxxxxxxxxxxxxxxx> wrote: >>> >>> OK, thanks. >>> >>> And for "kasan_depth == 1", I guess, its meaning is related with >>> kasan_depth[++|--] in kasan_[en|dis]able_current(): >> Assuming you are talking about the assignment of 1 to kasan_depth in >> /include/linux/init_task.h, >> it's somewhat counterintuitive. I think we just need to replace it >> with kasan_disable_current(), and add a corresponding >> kasan_enable_current() to the end of kasan_init. >> > > OK. But it does not look quite easy to use kasan_disable_current() for > INIT_KASAN which is used in INIT_TASK. > > If we have to set "kasan_depth == 1", we have to use kasan_depth-- in > kasan_enable_current(). Agreed, decrementing the counter in kasan_enable_current() is more natural. I can fix this together with the comments. >>> >>> OK, thanks. >>> >>> I guess, we are agree with each other: "We can both issue a WARNING and >>> prevent the actual overflow/underflow.". >> No, I am not sure think that we need to prevent the overflow. >> As I showed before, this may result in kasan_depth being off even in >> the case kasan_enable_current()/kasan_disable_current() are used >> consistently. > > If we don't prevent the overflow, it will have negative effect with the > caller. When we issue an warning, it means the caller's hope fail, but > can not destroy the caller's original work. In our case: > > - Assume "kasan_depth-- for kasan_enable_current()", the first enable > will let kasan_depth be 0. Sorry, I'm not sure I follow. If we start with kasan_depth=0 (which is the default case for every task except for the init, which also gets kasan_depth=0 short after the kernel starts), then the first call to kasan_disable_current() will make kasan_depth nonzero and will disable KASAN. The subsequent call to kasan_enable_current() will enable KASAN back. There indeed is a problem when someone calls kasan_enable_current() without previously calling kasan_disable_current(). In this case we need to check that kasan_depth was zero and print a warning if it was. It actually does not matter whether we modify kasan_depth after that warning or not, because we are already in inconsistent state. But I think we should modify kasan_depth anyway to ease the debugging. > - If we don't prevent the overflow, 2nd enable will cause disable > effect, which will destroy the caller's original work. The subsequent call to kasan_enable_current() will > - Enable/disable mismatch is caused by caller, we can issue warnings, > and skip it (since it is not caused by us). But we can not generate > new issues to the system only because of the caller's issue. > > > Thanks. > -- > Chen Gang (陈刚) > > Managing Natural Environments is the Duty of Human Beings. -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href