Commit c0fd2101 authored by Carlos Llamas's avatar Carlos Llamas Committed by Greg Kroah-Hartman
Browse files

Revert "android: binder: stop saving a pointer to the VMA" 

This reverts commit a43cfc87.

This patch fixed an issue reported by syzkaller in [1]. However, this
turned out to be only a band-aid in binder. The root cause, as bisected
by syzkaller, was fixed by commit 5789151e ("mm/mmap: undo ->mmap()
when mas_preallocate() fails"). We no longer need the patch for binder.

Reverting such patch allows us to have a lockless access to alloc->vma
in specific cases where the mmap_lock is not required. This approach
avoids the contention that caused a performance regression.

[1] https://lore.kernel.org/all/0000000000004a0dbe05e1d749e0@google.com



[cmllamas: resolved conflicts with rework of alloc->mm and removal of
 binder_alloc_set_vma() also fixed comment section]

Fixes: a43cfc87 ("android: binder: stop saving a pointer to the VMA")
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarCarlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20230502201220.1756319-2-cmllamas@google.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b15655b1

drivers/android/binder_alloc.c

+9 −8
Original line number Diff line number Diff line
@@ -213,7 +213,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate, 


	if (mm) {

		mmap_read_lock(mm);

		vma = vma_lookup(mm, alloc->vma_addr);

		vma = alloc->vma;

	}



	if (!vma && need_mm) {
@@ -314,9 +314,11 @@ static inline struct vm_area_struct *binder_alloc_get_vma( 
{

	struct vm_area_struct *vma = NULL;



	if (alloc->vma_addr)

		vma = vma_lookup(alloc->mm, alloc->vma_addr);



	if (alloc->vma) {

		/* Look at description in binder_alloc_set_vma */

		smp_rmb();

		vma = alloc->vma;

	}

	return vma;

}
@@ -775,7 +777,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc, 
	buffer->free = 1;

	binder_insert_free_buffer(alloc, buffer);

	alloc->free_async_space = alloc->buffer_size / 2;

	alloc->vma_addr = vma->vm_start;

	alloc->vma = vma;



	return 0;
@@ -805,8 +807,7 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc) 


	buffers = 0;

	mutex_lock(&alloc->mutex);

	BUG_ON(alloc->vma_addr &&

	       vma_lookup(alloc->mm, alloc->vma_addr));

	BUG_ON(alloc->vma);



	while ((n = rb_first(&alloc->allocated_buffers))) {

		buffer = rb_entry(n, struct binder_buffer, rb_node);
@@ -958,7 +959,7 @@ int binder_alloc_get_allocated_count(struct binder_alloc *alloc) 
 */

void binder_alloc_vma_close(struct binder_alloc *alloc)

{

	alloc->vma_addr = 0;

	alloc->vma = 0;

}



/**

drivers/android/binder_alloc.h

+2 −2
Original line number Diff line number Diff line
@@ -75,7 +75,7 @@ struct binder_lru_page { 
/**

 * struct binder_alloc - per-binder proc state for binder allocator

 * @mutex:              protects binder_alloc fields

 * @vma_addr:           vm_area_struct->vm_start passed to mmap_handler

 * @vma:                vm_area_struct passed to mmap_handler

 *                      (invariant after mmap)

 * @mm:                 copy of task->mm (invariant after open)

 * @buffer:             base of per-proc address space mapped via mmap
@@ -99,7 +99,7 @@ struct binder_lru_page { 
 */

struct binder_alloc {

	struct mutex mutex;

	unsigned long vma_addr;

	struct vm_area_struct *vma;

	struct mm_struct *mm;

	void __user *buffer;

	struct list_head buffers;

drivers/android/binder_alloc_selftest.c

+1 −1
Original line number Diff line number Diff line
@@ -287,7 +287,7 @@ void binder_selftest_alloc(struct binder_alloc *alloc) 
	if (!binder_selftest_run)

		return;

	mutex_lock(&binder_selftest_lock);

	if (!binder_selftest_run || !alloc->vma_addr)

	if (!binder_selftest_run || !alloc->vma)

		goto done;

	pr_info("STARTED\n");

	binder_selftest_alloc_offset(alloc, end_offset, 0);