On Mon, Nov 21, 2022 at 11:48:40AM -0800, Andrew Morton wrote: > On Mon, 21 Nov 2022 12:21:30 +0100 Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > > When aops->write_begin() does not initialize fsdata, KMSAN reports > > an error passing the latter to aops->write_end(). > > > > Fix this by unconditionally initializing fsdata. > > > > ... > > > > I'm assuming that this is not-a-bug, and that these changes are purely > workarounds for a KMSAN shortcoming? It's a weird one. It used to be not-a-bug. Then we changed from std=gnu99 to std=gnu11 or something. And in the intervening years, the C standards ctte decided that passing an uninitialised pointer to a function was UB. So we start by passing a pointer to the pointer to ->write_begin(). Some ->write_begin functions initialise that pointer; others don't. Then we pass the pointer directly to ->write_end. If ->write_begin initialised the pointer, that's fine, and if not, it's UB. Of course the ->write_end doesn't use it if the ->write_begin didn't initialise it, but it's too late because merely calling the function was UB. Thanks, Itanium!
