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btrfs-progs: kernel-lib: sync lib/rbtree.c 

Changes: comments, WRITE_ONCE, typos
Not included: RCU helpers

Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2022-05-12 13:07:15 +02:00
parent 68d04374f7
commit e49441a953
1 changed files with 105 additions and 45 deletions
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150
kernel-lib/rbtree.c
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@ -24,7 +24,7 @@
#include "kernel-lib/rbtree_augmented.h"
/*
* red-black trees properties: http://en.wikipedia.org/wiki/Rbtree
* red-black trees properties: https://en.wikipedia.org/wiki/Rbtree
*
* 1) A node is either red or black
* 2) The root is black
@ -43,6 +43,30 @@
* parentheses and have some accompanying text comment.
*/
/*
* Notes on lockless lookups:
*
* All stores to the tree structure (rb_left and rb_right) must be done using
* WRITE_ONCE(). And we must not inadvertently cause (temporary) loops in the
* tree structure as seen in program order.
*
* These two requirements will allow lockless iteration of the tree -- not
* correct iteration mind you, tree rotations are not atomic so a lookup might
* miss entire subtrees.
*
* But they do guarantee that any such traversal will only see valid elements
* and that it will indeed complete -- does not get stuck in a loop.
*
* It also guarantees that if the lookup returns an element it is the 'correct'
* one. But not returning an element does _NOT_ mean it's not present.
*
* NOTE:
*
* Stores to __rb_parent_color are not important for simple lookups so those
* are left undone as of now. Nor did I check for loops involving parent
* pointers.
*/
static inline void rb_set_black(struct rb_node *rb)
{
rb->__rb_parent_color |= RB_BLACK;
@ -76,16 +100,25 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
while (true) {
/*
* Loop invariant: node is red
*
* If there is a black parent, we are done.
* Otherwise, take some corrective action as we don't
* want a red root or two consecutive red nodes.
* Loop invariant: node is red.
*/
if (!parent) {
/*
* The inserted node is root. Either this is the
* first node, or we recursed at Case 1 below and
* are no longer violating 4).
*/
rb_set_parent_color(node, NULL, RB_BLACK);
break;
} else if (rb_is_black(parent))
}
/*
* If there is a black parent, we are done.
* Otherwise, take some corrective action as,
* per 4), we don't want a red root or two
* consecutive red nodes.
*/
if(rb_is_black(parent))
break;
gparent = rb_red_parent(parent);
@ -94,7 +127,7 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
if (parent != tmp) { /* parent == gparent->rb_left */
if (tmp && rb_is_red(tmp)) {
/*
* Case 1 - color flips
* Case 1 - node's uncle is red (color flips).
*
* G g
* / \ / \
@ -117,7 +150,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
tmp = parent->rb_right;
if (node == tmp) {
/*
* Case 2 - left rotate at parent
* Case 2 - node's uncle is black and node is
* the parent's right child (left rotate at parent).
*
* G G
* / \ / \
@ -128,8 +162,9 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
* This still leaves us in violation of 4), the
* continuation into Case 3 will fix that.
*/
parent->rb_right = tmp = node->rb_left;
node->rb_left = parent;
tmp = node->rb_left;
WRITE_ONCE(parent->rb_right, tmp);
WRITE_ONCE(node->rb_left, parent);
if (tmp)
rb_set_parent_color(tmp, parent,
RB_BLACK);
@ -140,7 +175,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
}
/*
* Case 3 - right rotate at gparent
* Case 3 - node's uncle is black and node is
* the parent's left child (right rotate at gparent).
*
* G P
* / \ / \
@ -148,8 +184,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
* / \
* n U
*/
gparent->rb_left = tmp; /* == parent->rb_right */
parent->rb_right = gparent;
WRITE_ONCE(gparent->rb_left, tmp); /* == parent->rb_right */
WRITE_ONCE(parent->rb_right, gparent);
if (tmp)
rb_set_parent_color(tmp, gparent, RB_BLACK);
__rb_rotate_set_parents(gparent, parent, root, RB_RED);
@ -170,8 +206,9 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
tmp = parent->rb_left;
if (node == tmp) {
/* Case 2 - right rotate at parent */
parent->rb_left = tmp = node->rb_right;
node->rb_right = parent;
tmp = node->rb_right;
WRITE_ONCE(parent->rb_left, tmp);
WRITE_ONCE(node->rb_right, parent);
if (tmp)
rb_set_parent_color(tmp, parent,
RB_BLACK);
@ -182,8 +219,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
}
/* Case 3 - left rotate at gparent */
gparent->rb_right = tmp; /* == parent->rb_left */
parent->rb_left = gparent;
WRITE_ONCE(gparent->rb_right, tmp); /* == parent->rb_left */
WRITE_ONCE(parent->rb_left, gparent);
if (tmp)
rb_set_parent_color(tmp, gparent, RB_BLACK);
__rb_rotate_set_parents(gparent, parent, root, RB_RED);
@ -223,8 +260,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
* / \ / \
* Sl Sr N Sl
*/
parent->rb_right = tmp1 = sibling->rb_left;
sibling->rb_left = parent;
tmp1 = sibling->rb_left;
WRITE_ONCE(parent->rb_right, tmp1);
WRITE_ONCE(sibling->rb_left, parent);
rb_set_parent_color(tmp1, parent, RB_BLACK);
__rb_rotate_set_parents(parent, sibling, root,
RB_RED);
@ -268,15 +306,31 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
*
* (p) (p)
* / \ / \
* N S --> N Sl
* N S --> N sl
* / \ \
* sl Sr s
* sl Sr S
* \
* Sr
*
* Note: p might be red, and then both
* p and sl are red after rotation(which
* breaks property 4). This is fixed in
* Case 4 (in __rb_rotate_set_parents()
* which set sl the color of p
* and set p RB_BLACK)
*
* (p) (sl)
* / \ / \
* N sl --> P S
* \ / \
* S N Sr
* \
* Sr
*/
sibling->rb_left = tmp1 = tmp2->rb_right;
tmp2->rb_right = sibling;
parent->rb_right = tmp2;
tmp1 = tmp2->rb_right;
WRITE_ONCE(sibling->rb_left, tmp1);
WRITE_ONCE(tmp2->rb_right, sibling);
WRITE_ONCE(parent->rb_right, tmp2);
if (tmp1)
rb_set_parent_color(tmp1, sibling,
RB_BLACK);
@ -296,8 +350,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
* / \ / \
* (sl) sr N (sl)
*/
parent->rb_right = tmp2 = sibling->rb_left;
sibling->rb_left = parent;
tmp2 = sibling->rb_left;
WRITE_ONCE(parent->rb_right, tmp2);
WRITE_ONCE(sibling->rb_left, parent);
rb_set_parent_color(tmp1, sibling, RB_BLACK);
if (tmp2)
rb_set_parent(tmp2, parent);
@ -309,8 +364,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
sibling = parent->rb_left;
if (rb_is_red(sibling)) {
/* Case 1 - right rotate at parent */
parent->rb_left = tmp1 = sibling->rb_right;
sibling->rb_right = parent;
tmp1 = sibling->rb_right;
WRITE_ONCE(parent->rb_left, tmp1);
WRITE_ONCE(sibling->rb_right, parent);
rb_set_parent_color(tmp1, parent, RB_BLACK);
__rb_rotate_set_parents(parent, sibling, root,
RB_RED);
@ -334,10 +390,11 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
}
break;
}
/* Case 3 - right rotate at sibling */
sibling->rb_right = tmp1 = tmp2->rb_left;
tmp2->rb_left = sibling;
parent->rb_left = tmp2;
/* Case 3 - left rotate at sibling */
tmp1 = tmp2->rb_left;
WRITE_ONCE(sibling->rb_right, tmp1);
WRITE_ONCE(tmp2->rb_left, sibling);
WRITE_ONCE(parent->rb_left, tmp2);
if (tmp1)
rb_set_parent_color(tmp1, sibling,
RB_BLACK);
@ -345,9 +402,10 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
tmp1 = sibling;
sibling = tmp2;
}
/* Case 4 - left rotate at parent + color flips */
parent->rb_left = tmp2 = sibling->rb_right;
sibling->rb_right = parent;
/* Case 4 - right rotate at parent + color flips */
tmp2 = sibling->rb_right;
WRITE_ONCE(parent->rb_left, tmp2);
WRITE_ONCE(sibling->rb_right, parent);
rb_set_parent_color(tmp1, sibling, RB_BLACK);
if (tmp2)
rb_set_parent(tmp2, parent);
@ -378,7 +436,9 @@ static inline void dummy_copy(struct rb_node *old, struct rb_node *new) {}
static inline void dummy_rotate(struct rb_node *old, struct rb_node *new) {}
static const struct rb_augment_callbacks dummy_callbacks = {
dummy_propagate, dummy_copy, dummy_rotate
.propagate = dummy_propagate,
.copy = dummy_copy,
.rotate = dummy_rotate
};
void rb_insert_color(struct rb_node *node, struct rb_root *root)
@ -446,9 +506,9 @@ struct rb_node *rb_next(const struct rb_node *node)
* as we can.
*/
if (node->rb_right) {
node = node->rb_right;
node = node->rb_right;
while (node->rb_left)
node=node->rb_left;
node = node->rb_left;
return (struct rb_node *)node;
}
@ -477,9 +537,9 @@ struct rb_node *rb_prev(const struct rb_node *node)
* as we can.
*/
if (node->rb_left) {
node = node->rb_left;
node = node->rb_left;
while (node->rb_right)
node=node->rb_right;
node = node->rb_right;
return (struct rb_node *)node;
}
@ -498,15 +558,15 @@ void rb_replace_node(struct rb_node *victim, struct rb_node *new,
{
struct rb_node *parent = rb_parent(victim);
/* Copy the pointers/colour from the victim to the replacement */
*new = *victim;
/* Set the surrounding nodes to point to the replacement */
__rb_change_child(victim, new, parent, root);
if (victim->rb_left)
rb_set_parent(victim->rb_left, new);
if (victim->rb_right)
rb_set_parent(victim->rb_right, new);
/* Copy the pointers/colour from the victim to the replacement */
*new = *victim;
__rb_change_child(victim, new, parent, root);
}
static struct rb_node *rb_left_deepest_node(const struct rb_node *node)