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Commit 1091e4b2 authored by Vinayak Menon's avatar Vinayak Menon Committed by Gerrit - the friendly Code Review server
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ANDROID: mm: use raw seqcount variants in vm_write_* 



write_seqcount_begin expects to be called from a non-preemptible
context to avoid preemption by a read section that can spin due
to an odd value. But the readers of vm_sequence never retries and
thus writers need not disable preemption. Use the non-lockdep
variant as lockdep checks are now in-built to write_seqcount_begin.

Bug: 161210518
Signed-off-by: default avatarVinayak Menon <vinmenon@codeaurora.org>
Change-Id: If4f0cddd7f0a79136495060d4acc1702abb46817
Git-commit: c9201630e8a53106406516ba40862e637c324480
Git-repo: https://android.googlesource.com/kernel/common/


Signed-off-by: default avatarSrinivasarao Pathipati <quic_spathi@quicinc.com>
parent 4bd53b87

include/linux/mm.h

+5 −24
Original line number Diff line number Diff line
@@ -1498,22 +1498,13 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr, 
#ifdef CONFIG_SPECULATIVE_PAGE_FAULT

static inline void vm_write_begin(struct vm_area_struct *vma)

{

	write_seqcount_begin(&vma->vm_sequence);

}

static inline void vm_write_begin_nested(struct vm_area_struct *vma,

					 int subclass)

{

	write_seqcount_begin_nested(&vma->vm_sequence, subclass);

}

static inline void vm_write_end(struct vm_area_struct *vma)

{

	write_seqcount_end(&vma->vm_sequence);

}

static inline void vm_raw_write_begin(struct vm_area_struct *vma)

{

	/*

	 * The reads never spins and preemption

	 * disablement is not required.

	 */

	raw_write_seqcount_begin(&vma->vm_sequence);

}

static inline void vm_raw_write_end(struct vm_area_struct *vma)

static inline void vm_write_end(struct vm_area_struct *vma)

{

	raw_write_seqcount_end(&vma->vm_sequence);

}
@@ -1521,19 +1512,9 @@ static inline void vm_raw_write_end(struct vm_area_struct *vma) 
static inline void vm_write_begin(struct vm_area_struct *vma)

{

}

static inline void vm_write_begin_nested(struct vm_area_struct *vma,

					 int subclass)

{

}

static inline void vm_write_end(struct vm_area_struct *vma)

{

}

static inline void vm_raw_write_begin(struct vm_area_struct *vma)

{

}

static inline void vm_raw_write_end(struct vm_area_struct *vma)

{

}

#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */



extern void truncate_pagecache(struct inode *inode, loff_t new);

mm/mmap.c

+9 −29
Original line number Diff line number Diff line
@@ -735,29 +735,9 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, 
	long adjust_next = 0;

	int remove_next = 0;



	/*

	 * Why using vm_raw_write*() functions here to avoid lockdep's warning ?

	 *

	 * Locked is complaining about a theoretical lock dependency, involving

	 * 3 locks:

	 *   mapping->i_mmap_rwsem --> vma->vm_sequence --> fs_reclaim

	 *

	 * Here are the major path leading to this dependency :

	 *  1. __vma_adjust() mmap_sem  -> vm_sequence -> i_mmap_rwsem

	 *  2. move_vmap() mmap_sem -> vm_sequence -> fs_reclaim

	 *  3. __alloc_pages_nodemask() fs_reclaim -> i_mmap_rwsem

	 *  4. unmap_mapping_range() i_mmap_rwsem -> vm_sequence

	 *

	 * So there is no way to solve this easily, especially because in

	 * unmap_mapping_range() the i_mmap_rwsem is grab while the impacted

	 * VMAs are not yet known.

	 * However, the way the vm_seq is used is guarantying that we will

	 * never block on it since we just check for its value and never wait

	 * for it to move, see vma_has_changed() and handle_speculative_fault().

	 */

	vm_raw_write_begin(vma);

	vm_write_begin(vma);

	if (next)

		vm_raw_write_begin(next);

		vm_write_begin(next);



	if (next && !insert) {

		struct vm_area_struct *exporter = NULL, *importer = NULL;
@@ -841,8 +821,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, 
			error = anon_vma_clone(importer, exporter);

			if (error) {

				if (next && next != vma)

					vm_raw_write_end(next);

				vm_raw_write_end(vma);

					vm_write_end(next);

				vm_write_end(vma);

				return error;

			}

		}
@@ -971,7 +951,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, 
		if (next->anon_vma)

			anon_vma_merge(vma, next);

		mm->map_count--;

		vm_raw_write_end(next);

		vm_write_end(next);

		put_vma(next);

		/*

		 * In mprotect's case 6 (see comments on vma_merge),
@@ -987,7 +967,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, 
			 */

			next = vma->vm_next;

			if (next)

				vm_raw_write_begin(next);

				vm_write_begin(next);

		} else {

			/*

			 * For the scope of the comment "next" and
@@ -1035,9 +1015,9 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, 
		uprobe_mmap(insert);



	if (next && next != vma)

		vm_raw_write_end(next);

		vm_write_end(next);

	if (!keep_locked)

		vm_raw_write_end(vma);

		vm_write_end(vma);



	validate_mm(mm);
@@ -3348,7 +3328,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, 
		 * that we protect it right now, and let the caller unprotect

		 * it once the move is done.

		 */

		vm_raw_write_begin(new_vma);

		vm_write_begin(new_vma);

		vma_link(mm, new_vma, prev, rb_link, rb_parent);

		*need_rmap_locks = false;

	}

mm/mremap.c

+4 −4
Original line number Diff line number Diff line
@@ -300,7 +300,7 @@ static unsigned long move_vma(struct vm_area_struct *vma, 
	 * to be mapped in our back while we are copying the PTEs.

	 */

	if (vma != new_vma)

		vm_raw_write_begin(vma);

		vm_write_begin(vma);



	moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,

				     need_rmap_locks);
@@ -319,7 +319,7 @@ static unsigned long move_vma(struct vm_area_struct *vma, 
		move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,

				 true);

		if (vma != new_vma)

			vm_raw_write_end(vma);

			vm_write_end(vma);

		vma = new_vma;

		old_len = new_len;

		old_addr = new_addr;
@@ -329,9 +329,9 @@ static unsigned long move_vma(struct vm_area_struct *vma, 
		arch_remap(mm, old_addr, old_addr + old_len,

			   new_addr, new_addr + new_len);

		if (vma != new_vma)

			vm_raw_write_end(vma);

			vm_write_end(vma);

	}

	vm_raw_write_end(new_vma);

	vm_write_end(new_vma);



	/* Conceal VM_ACCOUNT so old reservation is not undone */

	if (vm_flags & VM_ACCOUNT) {