On Mon, Mar 09, 2020 at 09:11:25PM +0100, Vlastimil Babka wrote: > On 3/9/2020 8:22 PM, gregkh@xxxxxxxxxxxxxxxxxxx wrote: > > > > This is a note to let you know that I've just added the patch titled > > > > mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled > > > > to the 5.4-stable tree which can be found at: > > http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary > > > > The filename of the patch is: > > mm-hotplug-fix-page-online-with-debug_pagealloc-compiled-but-not-enabled.patch > > and it can be found in the queue-5.4 subdirectory. > > > > If you, or anyone else, feels it should not be added to the stable tree, > > please let <stable@xxxxxxxxxxxxxxx> know about it. > > > > > > From c87cbc1f007c4b46165f05ceca04e1973cda0b9c Mon Sep 17 00:00:00 2001 > > From: Vlastimil Babka <vbabka@xxxxxxx> > > Date: Thu, 5 Mar 2020 22:28:42 -0800 > > Subject: mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled > > > > From: Vlastimil Babka <vbabka@xxxxxxx> > > > > commit c87cbc1f007c4b46165f05ceca04e1973cda0b9c upstream. > > > > Commit cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC") > > fixed memory hotplug with debug_pagealloc enabled, where onlining a page > > goes through page freeing, which removes the direct mapping. Some arches > > don't like when the page is not mapped in the first place, so > > generic_online_page() maps it first. This is somewhat wasteful, but > > better than special casing page freeing fast paths. > > > > The commit however missed that DEBUG_PAGEALLOC configured doesn't mean > > it's actually enabled. One has to test debug_pagealloc_enabled() since > > 031bc5743f15 ("mm/debug-pagealloc: make debug-pagealloc boottime > > configurable"), or alternatively debug_pagealloc_enabled_static() since > > 8e57f8acbbd1 ("mm, debug_pagealloc: don't rely on static keys too early"), > > but this is not done. > > > > As a result, a s390 kernel with DEBUG_PAGEALLOC configured but not enabled > > will crash: > > > > Unable to handle kernel pointer dereference in virtual kernel address space > > Failing address: 0000000000000000 TEID: 0000000000000483 > > Fault in home space mode while using kernel ASCE. > > AS:0000001ece13400b R2:000003fff7fd000b R3:000003fff7fcc007 S:000003fff7fd7000 P:000000000000013d > > Oops: 0004 ilc:2 [#1] SMP > > CPU: 1 PID: 26015 Comm: chmem Kdump: loaded Tainted: GX 5.3.18-5-default #1 SLE15-SP2 (unreleased) > > Krnl PSW : 0704e00180000000 0000001ecd281b9e (__kernel_map_pages+0x166/0x188) > > R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3 > > Krnl GPRS: 0000000000000000 0000000000000800 0000400b00000000 0000000000000100 > > 0000000000000001 0000000000000000 0000000000000002 0000000000000100 > > 0000001ece139230 0000001ecdd98d40 0000400b00000100 0000000000000000 > > 000003ffa17e4000 001fffe0114f7d08 0000001ecd4d93ea 001fffe0114f7b20 > > Krnl Code: 0000001ecd281b8e: ec17ffff00d8 ahik %r1,%r7,-1 > > 0000001ecd281b94: ec111dbc0355 risbg %r1,%r1,29,188,3 > >> 0000001ecd281b9e: 94fb5006 ni 6(%r5),251 > > 0000001ecd281ba2: 41505008 la %r5,8(%r5) > > 0000001ecd281ba6: ec51fffc6064 cgrj %r5,%r1,6,1ecd281b9e > > 0000001ecd281bac: 1a07 ar %r0,%r7 > > 0000001ecd281bae: ec03ff584076 crj %r0,%r3,4,1ecd281a5e > > Call Trace: > > [<0000001ecd281b9e>] __kernel_map_pages+0x166/0x188 > > [<0000001ecd4d9516>] online_pages_range+0xf6/0x128 > > [<0000001ecd2a8186>] walk_system_ram_range+0x7e/0xd8 > > [<0000001ecda28aae>] online_pages+0x2fe/0x3f0 > > [<0000001ecd7d02a6>] memory_subsys_online+0x8e/0xc0 > > [<0000001ecd7add42>] device_online+0x5a/0xc8 > > [<0000001ecd7d0430>] state_store+0x88/0x118 > > [<0000001ecd5b9f62>] kernfs_fop_write+0xc2/0x200 > > [<0000001ecd5064b6>] vfs_write+0x176/0x1e0 > > [<0000001ecd50676a>] ksys_write+0xa2/0x100 > > [<0000001ecda315d4>] system_call+0xd8/0x2c8 > > > > Fix this by checking debug_pagealloc_enabled_static() before calling > > kernel_map_pages(). Backports for kernel before 5.5 should use > > debug_pagealloc_enabled() instead. Also add comments. > > > > Fixes: cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC") > > Reported-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx> > > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> > > Cc: <stable@xxxxxxxxxxxxxxx> > > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > > Cc: Qian Cai <cai@xxxxxx> > > Link: http://lkml.kernel.org/r/20200224094651.18257-1-vbabka@xxxxxxx > > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > > > --- > > include/linux/mm.h | 4 ++++ > > mm/memory_hotplug.c | 8 +++++++- > > 2 files changed, 11 insertions(+), 1 deletion(-) > > > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -2695,6 +2695,10 @@ static inline bool debug_pagealloc_enabl > > #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP) > > extern void __kernel_map_pages(struct page *page, int numpages, int enable); > > > > +/* > > + * When called in DEBUG_PAGEALLOC context, the call should most likely be > > + * guarded by debug_pagealloc_enabled() or debug_pagealloc_enabled_static() > > + */ > > static inline void > > kernel_map_pages(struct page *page, int numpages, int enable) > > { > > --- a/mm/memory_hotplug.c > > +++ b/mm/memory_hotplug.c > > @@ -598,7 +598,13 @@ EXPORT_SYMBOL_GPL(__online_page_free); > > > > static void generic_online_page(struct page *page, unsigned int order) > > { > > - kernel_map_pages(page, 1 << order, 1); > > + /* > > + * Freeing the page with debug_pagealloc enabled will try to unmap it, > > + * so we should map it first. This is better than introducing a special > > + * case in page freeing fast path. > > + */ > > + if (debug_pagealloc_enabled_static()) > > Won't build on 5.4, see in changelog "Backports for kernel before 5.5 should use > debug_pagealloc_enabled() instead." Builds just fine for me here, are you _sure_ 5.4.y doesn't work? 5.4.14 got debug_pagealloc_enabled_static() through the backport of 8e57f8acbbd1 ("mm, debug_pagealloc: don't rely on static keys too early") which you wrote :) Now if it still needs to be changed, let me know and I will do so. thanks, greg k-h
