On 7/19/22 16:13, Andrew Morton wrote: > On Mon, 18 Jul 2022 16:26:25 +0200 Marco Elver <elver@xxxxxxxxxx> wrote: > >> On Sat, 16 Jul 2022 at 20:43, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: >> [...] >>>> - This patch has been accused of crashing the kernel: >>>> >>>> https://lkml.kernel.org/r/YsFeUHkrFTQ7T51Q@xsang-OptiPlex-9020 >>>> >>>> Do we think that report is bogus? >>> I think all of this is highly architecture-specific... >> The report can be reproduced on i386 with CONFIG_X86_PAE=y. But e.g. >> mm/memblock.c:memblock_free() is also guilty of using __pa() on >> previously memblock_alloc()'d addresses. Looking at the phys addr >> before memblock_alloc() does virt_to_phys(), the result of __pa() >> looks correct even on PAE, at least for the purpose of passing it on >> to kmemleak(). So I don't know what that BUG_ON(slow_virt_to_phys() != >> phys_addr) is supposed to tell us here. >> > It's only been nine years, so I'm sure Dave can remember why he added > it ;) > > BUG_ON(slow_virt_to_phys((void *)x) != phys_addr); > > in arch/x86/mm/physaddr.c:__phys_addr(). I think I intended it to double check that the linear map is *actually* a linear map for 'x'. Sure, we can use the "x - PAGE_OFFSET" shortcut, but did it turn out to be actually accurate for the address it was handed? I'd be curious what the page tables actually say for the address that's causing problems.
