mirror of
https://src.fedoraproject.org/rpms/grub2.git
synced 2024-11-24 06:22:43 +00:00
120 lines
3.3 KiB
Diff
120 lines
3.3 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
|
|
From: Daniel Axtens <dja@axtens.net>
|
|
Date: Thu, 25 Nov 2021 02:22:48 +1100
|
|
Subject: [PATCH] mm: Document grub_free()
|
|
|
|
The grub_free() possesses a surprising number of quirks, and also
|
|
uses single-letter variable names confusingly to iterate through
|
|
the free list.
|
|
|
|
Document what's going on.
|
|
|
|
Use prev and cur to iterate over the free list.
|
|
|
|
Signed-off-by: Daniel Axtens <dja@axtens.net>
|
|
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
|
|
(cherry picked from commit 1f8d0b01738e49767d662d6426af3570a64565f0)
|
|
---
|
|
grub-core/kern/mm.c | 63 ++++++++++++++++++++++++++++++++++-------------------
|
|
1 file changed, 41 insertions(+), 22 deletions(-)
|
|
|
|
diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c
|
|
index db7e0b2a5b..0351171cf9 100644
|
|
--- a/grub-core/kern/mm.c
|
|
+++ b/grub-core/kern/mm.c
|
|
@@ -446,54 +446,73 @@ grub_free (void *ptr)
|
|
}
|
|
else
|
|
{
|
|
- grub_mm_header_t q, s;
|
|
+ grub_mm_header_t cur, prev;
|
|
|
|
#if 0
|
|
- q = r->first;
|
|
+ cur = r->first;
|
|
do
|
|
{
|
|
grub_printf ("%s:%d: q=%p, q->size=0x%x, q->magic=0x%x\n",
|
|
- GRUB_FILE, __LINE__, q, q->size, q->magic);
|
|
- q = q->next;
|
|
+ GRUB_FILE, __LINE__, cur, cur->size, cur->magic);
|
|
+ cur = cur->next;
|
|
}
|
|
- while (q != r->first);
|
|
+ while (cur != r->first);
|
|
#endif
|
|
-
|
|
- for (s = r->first, q = s->next; q <= p || q->next >= p; s = q, q = s->next)
|
|
+ /* Iterate over all blocks in the free ring.
|
|
+ *
|
|
+ * The free ring is arranged from high addresses to low
|
|
+ * addresses, modulo wraparound.
|
|
+ *
|
|
+ * We are looking for a block with a higher address than p or
|
|
+ * whose next address is lower than p.
|
|
+ */
|
|
+ for (prev = r->first, cur = prev->next; cur <= p || cur->next >= p;
|
|
+ prev = cur, cur = prev->next)
|
|
{
|
|
- if (q->magic != GRUB_MM_FREE_MAGIC)
|
|
- grub_fatal ("free magic is broken at %p: 0x%x", q, q->magic);
|
|
+ if (cur->magic != GRUB_MM_FREE_MAGIC)
|
|
+ grub_fatal ("free magic is broken at %p: 0x%x", cur, cur->magic);
|
|
|
|
- if (q <= q->next && (q > p || q->next < p))
|
|
+ /* Deal with wrap-around */
|
|
+ if (cur <= cur->next && (cur > p || cur->next < p))
|
|
break;
|
|
}
|
|
|
|
+ /* mark p as free and insert it between cur and cur->next */
|
|
p->magic = GRUB_MM_FREE_MAGIC;
|
|
- p->next = q->next;
|
|
- q->next = p;
|
|
+ p->next = cur->next;
|
|
+ cur->next = p;
|
|
|
|
+ /*
|
|
+ * If the block we are freeing can be merged with the next
|
|
+ * free block, do that.
|
|
+ */
|
|
if (p->next + p->next->size == p)
|
|
{
|
|
p->magic = 0;
|
|
|
|
p->next->size += p->size;
|
|
- q->next = p->next;
|
|
+ cur->next = p->next;
|
|
p = p->next;
|
|
}
|
|
|
|
- r->first = q;
|
|
+ r->first = cur;
|
|
|
|
- if (q == p + p->size)
|
|
+ /* Likewise if can be merged with the preceeding free block */
|
|
+ if (cur == p + p->size)
|
|
{
|
|
- q->magic = 0;
|
|
- p->size += q->size;
|
|
- if (q == s)
|
|
- s = p;
|
|
- s->next = p;
|
|
- q = s;
|
|
+ cur->magic = 0;
|
|
+ p->size += cur->size;
|
|
+ if (cur == prev)
|
|
+ prev = p;
|
|
+ prev->next = p;
|
|
+ cur = prev;
|
|
}
|
|
|
|
- r->first = q;
|
|
+ /*
|
|
+ * Set r->first such that the just free()d block is tried first.
|
|
+ * (An allocation is tried from *first->next, and cur->next == p.)
|
|
+ */
|
|
+ r->first = cur;
|
|
}
|
|
}
|
|
|