Re: [PATCH 03/16] page-flags: introduce page flags policies wrt compound pages

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Fri, Sep 25, 2015 at 03:29:17PM +0300, Konstantin Khlebnikov wrote:
> On 24.09.2015 17:50, Kirill A. Shutemov wrote:
> >This patch adds a third argument to macros which create function
> >definitions for page flags.  This argument defines how page-flags helpers
> >behave on compound functions.
> >
> >For now we define four policies:
> >
> >- PF_ANY: the helper function operates on the page it gets, regardless
> >   if it's non-compound, head or tail.
> >
> >- PF_HEAD: the helper function operates on the head page of the compound
> >   page if it gets tail page.
> >
> >- PF_NO_TAIL: only head and non-compond pages are acceptable for this
> >   helper function.
> >
> >- PF_NO_COMPOUND: only non-compound pages are acceptable for this helper
> >   function.
> >
> >For now we use policy PF_ANY for all helpers, which matches current
> >behaviour.
> >
> >We do not enforce the policy for TESTPAGEFLAG, because we have flags
> >checked for random pages all over the kernel.  Noticeable exception to
> >this is PageTransHuge() which triggers VM_BUG_ON() for tail page.
> >
> >Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> >---
> >  include/linux/page-flags.h | 154 ++++++++++++++++++++++++++-------------------
> >  1 file changed, 90 insertions(+), 64 deletions(-)
> >
> >diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> >index 713d3f2c2468..1b3babe5ff69 100644
> >--- a/include/linux/page-flags.h
> >+++ b/include/linux/page-flags.h
> >@@ -154,49 +154,68 @@ static inline int PageCompound(struct page *page)
> >  	return test_bit(PG_head, &page->flags) || PageTail(page);
> >  }
> >
> >+/* Page flags policies wrt compound pages */
> >+#define PF_ANY(page, enforce)	page
> >+#define PF_HEAD(page, enforce)	compound_head(page)
> >+#define PF_NO_TAIL(page, enforce) ({					\
> >+		if (enforce)						\
> >+			VM_BUG_ON_PAGE(PageTail(page), page);		\
> >+		else							\
> >+			page = compound_head(page);			\
> >+		page;})
> >+#define PF_NO_COMPOUND(page, enforce) ({					\
> >+		if (enforce)						\
> >+			VM_BUG_ON_PAGE(PageCompound(page), page);	\
> 
> Linux next-20150925 crashes here (at least in lkvm)
> if CONFIG_DEFERRED_STRUCT_PAGE_INIT=y

Hm. I don't see the crash in qemu. Could you share your config?

> [    0.000000] Kernel command line: noapic noacpi pci=conf1 reboot=k panic=1
> i8042.direct=1 i8042.dumbkbd=1 i8042.nopnp=1 console=ttyS0
> earlyprintk=serial i8042.noaux=1  root=/dev/root rw
> rootflags=rw,trans=virtio,version=9p2000.L rootfstype=9p init=/virt/init
> ip=dhcp
> [    0.000000] PID hash table entries: 2048 (order: 2, 16384 bytes)
> [    0.000000] BUG: unable to handle kernel NULL pointer dereference at
> 000000000000000c
> [    0.000000] IP: [<ffffffff811aaafb>] dump_page_badflags+0x2b/0xe0
> [    0.000000] PGD 0
> [    0.000000] Oops: 0000 [#1] SMP
> [    0.000000] Modules linked in:
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted
> 4.3.0-rc2-next-20150925+ #2
> [    0.000000] task: ffffffff81c12580 ti: ffffffff81c00000 task.ti:
> ffffffff81c00000
> [    0.000000] RIP: 0010:[<ffffffff811aaafb>]  [<ffffffff811aaafb>]
> dump_page_badflags+0x2b/0xe0
> [    0.000000] RSP: 0000:ffffffff81c03ea8  EFLAGS: 00010002
> [    0.000000] RAX: 000000000000000c RBX: ffffea00006dfd40 RCX:
> 0000000000000100
> [    0.000000] RDX: 0000000000000001 RSI: ffffffff81a4aeb8 RDI:
> ffffea00006dfd40
> [    0.000000] RBP: ffffffff81c03ec0 R08: 0000000000000000 R09:
> 0000000000000000
> [    0.000000] R10: 0000000000000001 R11: 0000000000000000 R12:
> 0000000000000000
> [    0.000000] R13: 000000000001b7f7 R14: ffffffff81fe50c0 R15:
> ffffffff81c03fb0
> [    0.000000] FS:  0000000000000000(0000) GS:ffff88001a400000(0000)
> knlGS:0000000000000000
> [    0.000000] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    0.000000] CR2: 000000000000000c CR3: 0000000001c0b000 CR4:
> 00000000000406b0
> [    0.000000] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [    0.000000] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400
> [    0.000000] Stack:
> [    0.000000]  000000000001b7f5 ffffea00006dfd40 000000000001b7f7
> ffffffff81c03ed0
> [    0.000000]  ffffffff811aabc0 ffffffff81c03ef8 ffffffff81785eda
> ffffffff81c03f10
> [    0.000000]  0000000000000040 ffffffff81fd99c0 ffffffff81c03f30
> ffffffff81f66600
> [    0.000000] Call Trace:
> [    0.000000]  [<ffffffff811aabc0>] dump_page+0x10/0x20
> [    0.000000]  [<ffffffff81785eda>] reserve_bootmem_region+0xd9/0xe2
> [    0.000000]  [<ffffffff81f66600>] free_all_bootmem+0x4b/0x11a
> [    0.000000]  [<ffffffff81f5428d>] mem_init+0x6a/0x9d
> [    0.000000]  [<ffffffff81f37d48>] start_kernel+0x214/0x46a
> [    0.000000]  [<ffffffff81f37120>] ? early_idt_handler_array+0x120/0x120
> [    0.000000]  [<ffffffff81f374d7>] x86_64_start_reservations+0x2a/0x2c
> [    0.000000]  [<ffffffff81f3760f>] x86_64_start_kernel+0x136/0x145
> [    0.000000] Code: e8 3b 7b 5e 00 55 48 89 e5 41 55 41 54 49 89 d4 53 48
> 8b 57 20 48 89 fb 4c 8b 4f 10 4c 8b 47 08 48 8d 42 ff 83 e2 01 48 0f 44 c7
> <48> 8b 00 a8 80 75 4b 8b 4f 18 8b 57 1c 49 89 f5 31 c0 48 89 fe
> [    0.000000] RIP  [<ffffffff811aaafb>] dump_page_badflags+0x2b/0xe0
> [    0.000000]  RSP <ffffffff81c03ea8>
> [    0.000000] CR2: 000000000000000c
> [    0.000000] ---[ end trace cb88537fdc8fa200 ]---

Could you try this:

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9bcfd70b1eb8..eff685f83879 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -929,8 +929,6 @@ static void init_reserved_page(unsigned long pfn)
 #else
 static inline void init_reserved_page(unsigned long pfn)
 {
-       /* Avoid false-positive PageTail() */
-       INIT_LIST_HEAD(&pfn_to_page(pfn)->lru);
 }
 #endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
 
@@ -950,6 +948,10 @@ void __meminit reserve_bootmem_region(unsigned long start, unsigned long end)
                        struct page *page = pfn_to_page(start_pfn);
 
                        init_reserved_page(start_pfn);
+
+                       /* Avoid false-positive PageTail() */
+                       INIT_LIST_HEAD(&pfn_to_page(pfn)->lru);
+
                        SetPageReserved(page);
                }
        }
-- 
 Kirill A. Shutemov

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