path: root/arch
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authorKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2011-11-15 14:49:09 -0800
committerIngo Molnar <mingo@elte.hu>2011-12-05 17:06:34 +0100
commit2cd1c8d4dc7ecca9e9431e2dabe41ae9c7d89e51 (patch)
tree7ab077a7854d5f2371030d2080ee8db10ded9a69 /arch
parentf1b23714cb578c88ea051768bf26b459e1264411 (diff)
x86/paravirt: PTE updates in k(un)map_atomic need to be synchronous, regardless of lazy_mmu mode
Fix an outstanding issue that has been reported since 2.6.37. Under a heavy loaded machine processing "fork()" calls could crash with: BUG: unable to handle kernel paging request at f573fc8c IP: [<c01abc54>] swap_count_continued+0x104/0x180 *pdpt = 000000002a3b9027 *pde = 0000000001bed067 *pte = 0000000000000000 Oops: 0000 [#1] SMP Modules linked in: Pid: 1638, comm: apache2 Not tainted 3.0.4-linode37 #1 EIP: 0061:[<c01abc54>] EFLAGS: 00210246 CPU: 3 EIP is at swap_count_continued+0x104/0x180 .. snip.. Call Trace: [<c01ac222>] ? __swap_duplicate+0xc2/0x160 [<c01040f7>] ? pte_mfn_to_pfn+0x87/0xe0 [<c01ac2e4>] ? swap_duplicate+0x14/0x40 [<c01a0a6b>] ? copy_pte_range+0x45b/0x500 [<c01a0ca5>] ? copy_page_range+0x195/0x200 [<c01328c6>] ? dup_mmap+0x1c6/0x2c0 [<c0132cf8>] ? dup_mm+0xa8/0x130 [<c013376a>] ? copy_process+0x98a/0xb30 [<c013395f>] ? do_fork+0x4f/0x280 [<c01573b3>] ? getnstimeofday+0x43/0x100 [<c010f770>] ? sys_clone+0x30/0x40 [<c06c048d>] ? ptregs_clone+0x15/0x48 [<c06bfb71>] ? syscall_call+0x7/0xb The problem is that in copy_page_range() we turn lazy mode on, and then in swap_entry_free() we call swap_count_continued() which ends up in: map = kmap_atomic(page, KM_USER0) + offset; and then later we touch *map. Since we are running in batched mode (lazy) we don't actually set up the PTE mappings and the kmap_atomic is not done synchronously and ends up trying to dereference a page that has not been set. Looking at kmap_atomic_prot_pfn(), it uses 'arch_flush_lazy_mmu_mode' and doing the same in kmap_atomic_prot() and __kunmap_atomic() makes the problem go away. Interestingly, commit b8bcfe997e4615 ("x86/paravirt: remove lazy mode in interrupts") removed part of this to fix an interrupt issue - but it went to far and did not consider this scenario. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch')
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/x86/mm/highmem_32.c b/arch/x86/mm/highmem_32.c
index b4996266210..f4f29b19fac 100644
--- a/arch/x86/mm/highmem_32.c
+++ b/arch/x86/mm/highmem_32.c
@@ -45,6 +45,7 @@ void *kmap_atomic_prot(struct page *page, pgprot_t prot)
vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
set_pte(kmap_pte-idx, mk_pte(page, prot));
+ arch_flush_lazy_mmu_mode();
return (void *)vaddr;
@@ -88,6 +89,7 @@ void __kunmap_atomic(void *kvaddr)
kpte_clear_flush(kmap_pte-idx, vaddr);
+ arch_flush_lazy_mmu_mode();
else {