On Tue, Dec 01, 2020 at 12:42:39PM -0800, Dan Williams wrote: > On Mon, Nov 30, 2020 at 6:24 PM Matthew Wilcox <wi...@infradead.org> wrote: > > > > On Mon, Nov 30, 2020 at 05:20:25PM -0800, Dan Williams wrote: > > > Kirill, Willy, compound page experts, > > > > > > I am seeking some debug ideas about the following splat: > > > > > > BUG: Bad page state in process lt-pmem-ns pfn:121a12 > > > page:0000000051ef73f7 refcount:0 mapcount:-1024 > > > mapping:0000000000000000 index:0x0 pfn:0x121a12 > > > > Mapcount of -1024 is the signature of: > > > > #define PG_guard 0x00000400 > > Oh, thanks for that. I overlooked how mapcount is overloaded. Although > in v5.10-rc4 that value is: > > #define PG_table 0x00000400
Ah, I was looking at -next, where Roman renumbered it. I know UML had a problem where it was not clearing PG_table, but you seem to be running on bare metal. SuperH did too, but again, you're not using SuperH. > > > > (the bits are inverted, so this turns into 0xfffffbff which is reported > > as -1024) > > > > I assume you have debug_pagealloc enabled? > > Added it, but no extra spew. I'll dig a bit more on how PG_table is > not being cleared in this case. I only asked about debug_pagealloc because that sets PG_guard. Since the problem is actually PG_table, it's not relevant.
