On Tue, Oct 03, 2017 at 09:54:31AM -0700, Linus Torvalds wrote: > On Tue, Oct 3, 2017 at 7:06 AM, Fengguang Wu <fengguang...@intel.com> wrote: > > > > This patch triggers a NULL-dereference bug at update_stack_state(). > > Although its parent commit also has a NULL-dereference bug, however > > the call stack looks rather different. Both dmesg files are attached. > > > > It also triggers this warning, which is being discussed in another > > thread, so CC Josh. The full dmesg attached, too. > > > > Please press Enter to activate this console. > > [ 138.605622] WARNING: kernel stack regs at be299c9a in procd:340 > > has bad 'bp' value 000001be > > [ 138.605627] unwind stack type:0 next_sp: (null) mask:0x2 > > graph_idx:0 > > [ 138.605631] be299c9a: 299ceb00 (0x299ceb00) > > [ 138.605633] be299c9e: 2281f1be (0x2281f1be) > > [ 138.605634] be299ca2: 299cebb6 (0x299cebb6) > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master > > > > commit b09be676e0ff25bd6d2e7637e26d349f9109ad75 > > locking/lockdep: Implement the 'crossrelease' feature > > Can we consider just reverting the crossrelease thing? > > The apparent stack corruption really worries me, and what worries me > most is that commit wasn't even supposed to change anything as far as > I can tell - it only adds infrastructure, no actual users that *set* > the cross-lock thing. > > So the fact that it actually seems to cause behavioural changes seems > to be _really_ scary, and indicates that the code is completely > broken. > > Or am I missing something?
So I gave crossrelease a bad rap here. Going back and looking at the panics and stack dumps, what I thought was "stack corruption" was actually the GCC unaligned stack pointer thing. I suspect those commits were implicated in the bisections because they started doing more stack traces in general, revealing some existing 32-bit unwinder/GCC/frame pointer bugs in the process. So I just wanted to clarify that crossrelease seems to be innocent in all this. Sorry for the confusion! -- Josh
