From: Andrew Morton <akpm@linux-foundation.org>
Date: Wed, 1 Jun 2022 22:17:52 +0000 (-0700)
Subject: mm-drop-oom-code-from-exit_mmap-fix-fix
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=6d3676e230a22e61500b0bada85ad56e8142a2f0;p=users%2Fjedix%2Flinux-maple.git

mm-drop-oom-code-from-exit_mmap-fix-fix

restore Suren's mmap_read_lock() optimization

Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/mmap.c b/mm/mmap.c
index 8e85d06f0c2e..be111bbe8075 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3085,13 +3085,13 @@ void exit_mmap(struct mm_struct *mm)
 	/* mm's last user has gone, and its about to be pulled down */
 	mmu_notifier_release(mm);
 
-	mmap_write_lock(mm);
+	mmap_read_lock(mm);
 	arch_exit_mmap(mm);
 
 	vma = mas_find(&mas, ULONG_MAX);
 	if (!vma) {
 		/* Can happen if dup_mmap() received an OOM */
-		mmap_write_unlock(mm);
+		mmap_read_unlock(mm);
 		return;
 	}
 
@@ -3101,6 +3101,7 @@ void exit_mmap(struct mm_struct *mm)
 	/* update_hiwater_rss(mm) here? but nobody should be looking */
 	/* Use ULONG_MAX here to ensure all VMAs in the mm are unmapped */
 	unmap_vmas(&tlb, &mm->mm_mt, vma, 0, ULONG_MAX);
+	mmap_read_unlock(mm);
 
 	/*
 	 * Set MMF_OOM_SKIP to hide this task from the oom killer/reaper
@@ -3108,6 +3109,7 @@ void exit_mmap(struct mm_struct *mm)
 	 * mm_is_oom_victim because setting a bit unconditionally is cheaper.
 	 */
 	set_bit(MMF_OOM_SKIP, &mm->flags);
+	mmap_write_lock(mm);
 	free_pgtables(&tlb, &mm->mm_mt, vma, FIRST_USER_ADDRESS,
 		      USER_PGTABLES_CEILING);
 	tlb_finish_mmu(&tlb);