Dear Andrew, all, First of all, thank you for looking at the patch.
I do agree that if mm is NULL, system will call Oops anyway. However, since it's oops, it does not stop the system, nor call kdump. By calling BUG_ON(), it'll gives us chance of calling kdump at the first chance. Since this is very rare to happen, I thought we should capture the incident whenever possible. On other hand, because BUG_ON macro is very light, I thought this will not harm any performance... Forgive me in advance if I was wrong. I still think checking mm with BUG_ON here is better than counting on Oops. best regards, 2008/2/1, Andrew Morton <[EMAIL PROTECTED]>: > On Fri, 1 Feb 2008 16:39:07 +0900 "Kenichi Okuyama" <[EMAIL PROTECTED]> wrote: > > > Dear all, > > > > I was looking at the ./mm/rmap.c .. I found that, in function > > "page_referenced_one()", > > struct mm_struct *mm = vma->vm_mm; > > was being refererred without NULL check. > > > > Though I do agree that this works for most of the cases, I thought it > > is better to add > > BUG_ON() for case of mm being NULL. > > > > attached is the patch for this > > If we dereference NULL then the kernel will display basically the same > information as would a BUG, and it takes the same action. So adding a > BUG_ON here really doesn't gain us anything. > > Also, I think vma->vm_mm == 0 is not a valid state, so this just shouldn't > happen - the code is OK to assume that a particular invariant is being > honoured. > > -- 奥山 健一(Kenichi Okuyama) [煤背会: No. 0x00000001] URL: http://www.dd.iij4u.or.jp/~okuyamak/ http://developer.osdl.jp/projects/doubt/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
