linux-kernel - [PATCH v4 21/33] mm/mmap: prevent pagefault handler from racing with mmu

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Date:   Mon, 27 Feb 2023 09:36:20 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
        vbabka@...e.cz, hannes@...xchg.org, mgorman@...hsingularity.net,
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        peterz@...radead.org, ldufour@...ux.ibm.com, paulmck@...nel.org,
        mingo@...hat.com, will@...nel.org, luto@...nel.org,
        songliubraving@...com, peterx@...hat.com, david@...hat.com,
        dhowells@...hat.com, hughd@...gle.com, bigeasy@...utronix.de,
        kent.overstreet@...ux.dev, punit.agrawal@...edance.com,
        lstoakes@...il.com, peterjung1337@...il.com, rientjes@...gle.com,
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        gthelen@...gle.com, gurua@...gle.com, arjunroy@...gle.com,
        soheil@...gle.com, leewalsh@...gle.com, posk@...gle.com,
        michalechner92@...glemail.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: [PATCH v4 21/33] mm/mmap: prevent pagefault handler from racing with
 mmu_notifier registration

Page fault handlers might need to fire MMU notifications while a new
notifier is being registered. Modify mm_take_all_locks to write-lock all
VMAs and prevent this race with page fault handlers that would hold VMA
locks. VMAs are locked before i_mmap_rwsem and anon_vma to keep the same
locking order as in page fault handlers.

Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
 mm/mmap.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index ec745586785c..b947d82e8522 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3486,6 +3486,7 @@ static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
  * of mm/rmap.c:
  *   - all hugetlbfs_i_mmap_rwsem_key locks (aka mapping->i_mmap_rwsem for
  *     hugetlb mapping);
+ *   - all vmas marked locked
  *   - all i_mmap_rwsem locks;
  *   - all anon_vma->rwseml
  *
@@ -3508,6 +3509,13 @@ int mm_take_all_locks(struct mm_struct *mm)
 
 	mutex_lock(&mm_all_locks_mutex);
 
+	mas_for_each(&mas, vma, ULONG_MAX) {
+		if (signal_pending(current))
+			goto out_unlock;
+		vma_start_write(vma);
+	}
+
+	mas_set(&mas, 0);
 	mas_for_each(&mas, vma, ULONG_MAX) {
 		if (signal_pending(current))
 			goto out_unlock;
@@ -3597,6 +3605,7 @@ void mm_drop_all_locks(struct mm_struct *mm)
 		if (vma->vm_file && vma->vm_file->f_mapping)
 			vm_unlock_mapping(vma->vm_file->f_mapping);
 	}
+	vma_end_write_all(mm);
 
 	mutex_unlock(&mm_all_locks_mutex);
 }
-- 
2.39.2.722.g9855ee24e9-goog