[patch 09/17] mm/khugepaged: fix might_sleep() warn with CONFIG_HIGHPTE=y

[akpm@linux-foundation.org]

From: Ville Syrjälä <ville.syrjala@linux.intel.com>
Subject: mm/khugepaged: fix might_sleep() warn with CONFIG_HIGHPTE=y

I got some khugepaged spew on a 32bit x86:

[  217.490026] BUG: sleeping function called from invalid context at include/linux/mmu_notifier.h:346
[  217.492826] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 25, name: khugepaged
[  217.495589] INFO: lockdep is turned off.
[  217.498371] CPU: 1 PID: 25 Comm: khugepaged Not tainted 5.4.0-rc5-elk+ #206
[  217.501233] Hardware name: System manufacturer P5Q-EM/P5Q-EM, BIOS 2203    07/08/2009
[  217.501697] Call Trace:
[  217.501697]  dump_stack+0x66/0x8e
[  217.501697]  ___might_sleep.cold.96+0x95/0xa6
[  217.501697]  __might_sleep+0x2e/0x80
[  217.501697]  collapse_huge_page.isra.51+0x5ac/0x1360
[  217.501697]  ? __alloc_pages_nodemask+0xec/0xf80
[  217.501697]  ? __alloc_pages_nodemask+0x191/0xf80
[  217.501697]  ? trace_hardirqs_on+0x4a/0xf0
[  217.501697]  khugepaged+0x9a9/0x20f0
[  217.501697]  ? _raw_spin_unlock+0x21/0x30
[  217.501697]  ? trace_hardirqs_on+0x4a/0xf0
[  217.501697]  ? wait_woken+0xa0/0xa0
[  217.501697]  kthread+0xf5/0x110
[  217.501697]  ? collapse_pte_mapped_thp+0x3b0/0x3b0
[  217.501697]  ? kthread_create_worker_on_cpu+0x20/0x20
[  217.501697]  ret_from_fork+0x2e/0x38

Looks like it's due to CONFIG_HIGHPTE=y pte_offset_map()->kmap_atomic()
vs.  mmu_notifier_invalidate_range_start().  Let's do the naive approach
and just reorder the two operations.

Link: http://lkml.kernel.org/r/20191029201513.GG1208@intel.com
Fixes: 810e24e009cf71 ("mm/mmu_notifiers: annotate with might_sleep()")
Signed-off-by: Ville Syrjl <ville.syrjala@linux.intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/khugepaged.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/mm/khugepaged.c~khugepaged-might_sleep-warn-due-to-config_highpte=y
+++ a/mm/khugepaged.c
@@ -1028,12 +1028,13 @@ static void collapse_huge_page(struct mm
 
 	anon_vma_lock_write(vma->anon_vma);
 
-	pte = pte_offset_map(pmd, address);
-	pte_ptl = pte_lockptr(mm, pmd);
-
 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
 				address, address + HPAGE_PMD_SIZE);
 	mmu_notifier_invalidate_range_start(&range);
+
+	pte = pte_offset_map(pmd, address);
+	pte_ptl = pte_lockptr(mm, pmd);
+
 	pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
 	/*
 	 * After this gup_fast can't run anymore. This also removes
_