On Thu, Oct 03, 2019 at 01:32:50PM -0700, Matthew Wilcox wrote: > On Thu, Oct 03, 2019 at 01:18:47PM -0700, Davidlohr Bueso wrote: > > It has been discussed[1,2] that almost all users of interval trees would better > > be served if the intervals were actually not [a,b], but instead [a, b). This > > So how does a user represent a range from ULONG_MAX to ULONG_MAX now? > > I think the problem is that large parts of the kernel just don't consider > integer overflow. Because we write in C, it's natural to write: > > for (i = start; i < end; i++) > > and just assume that we never need to hit ULONG_MAX or UINT_MAX. > If we're storing addresses, that's generally true -- most architectures > don't allow addresses in the -PAGE_SIZE to ULONG_MAX range (or they'd > have trouble with PTR_ERR). If you're looking at file sizes, that's > not true on 32-bit machines, and we've definitely seen filesystem bugs > with files nudging up on 16TB (on 32 bit with 4k page size). Or block > driver bugs with similarly sized block devices. > > So, yeah, easier to use. But damning corner cases. Yeah, I wanted to ask - is the case where pgoff == ULONG_MAX (i.e., last block of a file that is exactly 16TB) currently supported on 32-bit archs ? I have no idea if I am supposed to care about this or not... -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies.
