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

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.

Cc: linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: "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: linux-mm@kvack.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
mm/khugepaged.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 0a1b4b484ac5..f05d27b7183d 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1028,12 +1028,13 @@ static void collapse_huge_page(struct mm_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
--
2.23.0
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