Commit e4bd84c0 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Linus Torvalds
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mm: Always downgrade mmap_lock if requested 



Now that stack growth must always hold the mmap_lock for write, we can
always downgrade the mmap_lock to read and safely unmap pages from the
page table, even if we're next to a stack.

Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 03f88937

mm/mmap.c

+2 −13
Original line number Diff line number Diff line
@@ -2551,19 +2551,8 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma, 
	/* Point of no return */

	mm->locked_vm -= locked_vm;

	mm->map_count -= count;

	/*

	 * Do not downgrade mmap_lock if we are next to VM_GROWSDOWN or

	 * VM_GROWSUP VMA. Such VMAs can change their size under

	 * down_read(mmap_lock) and collide with the VMA we are about to unmap.

	 */

	if (downgrade) {

		if (next && (next->vm_flags & VM_GROWSDOWN))

			downgrade = false;

		else if (prev && (prev->vm_flags & VM_GROWSUP))

			downgrade = false;

		else

	if (downgrade)

		mmap_write_downgrade(mm);

	}



	/*

	 * We can free page tables without write-locking mmap_lock because VMAs