+ z3fold-protect-handle-reads.patch added to -mm tree

[akpm@xxxxxxxxxxxxxxxxxxxx]

The patch titled
     Subject: z3fold: protect handle reads
has been added to the -mm tree.  Its filename is
     z3fold-protect-handle-reads.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/z3fold-protect-handle-reads.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/z3fold-protect-handle-reads.patch

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------------------------------------------------------
From: Vitaly Wool <vitalywool@xxxxxxxxx>
Subject: z3fold: protect handle reads

We need to make sure slots are protected on reading a handle.  Since
handles are modified by free_handle() which only takes slot rwlock, that
lock should be used when handles are read.

Link: http://lkml.kernel.org/r/20191127152345.8059852f60947686674d726d@xxxxxxxxx
Signed-off-by: Vitaly Wool <vitaly.vul@xxxxxxxx>
Cc: Dan Streetman <ddstreet@xxxxxxxx>
Cc: Henry Burns <henrywolfeburns@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/z3fold.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/mm/z3fold.c~z3fold-protect-handle-reads
+++ a/mm/z3fold.c
@@ -486,8 +486,12 @@ static unsigned long encode_handle(struc
 /* only for LAST bud, returns zero otherwise */
 static unsigned short handle_to_chunks(unsigned long handle)
 {
-	unsigned long addr = *(unsigned long *)handle;
+	struct z3fold_buddy_slots *slots = handle_to_slots(handle);
+	unsigned long addr;
 
+	read_lock(&slots->lock);
+	addr = *(unsigned long *)handle;
+	read_unlock(&slots->lock);
 	return (addr & ~PAGE_MASK) >> BUDDY_SHIFT;
 }
 
@@ -499,10 +503,13 @@ static unsigned short handle_to_chunks(u
 static enum buddy handle_to_buddy(unsigned long handle)
 {
 	struct z3fold_header *zhdr;
+	struct z3fold_buddy_slots *slots = handle_to_slots(handle);
 	unsigned long addr;
 
+	read_lock(&slots->lock);
 	WARN_ON(handle & (1 << PAGE_HEADLESS));
 	addr = *(unsigned long *)handle;
+	read_unlock(&slots->lock);
 	zhdr = (struct z3fold_header *)(addr & PAGE_MASK);
 	return (addr - zhdr->first_num) & BUDDY_MASK;
 }
_

Patches currently in -mm which might be from vitalywool@xxxxxxxxx are

z3fold-avoid-subtle-race-when-freeing-slots.patch
z3fold-compact-objects-more-accurately.patch
z3fold-protect-handle-reads.patch