Commit ba025082 authored by Tejun Heo's avatar Tejun Heo Committed by Linus Torvalds

[PATCH] blk: fix tag shrinking (revive real_max_size)

My patch in commit fa72b903 incorrectly
removed blk_queue_tag->real_max_depth.

The original resize implementation was incorrect in the following

 * actual allocation size of tag_index was shorter than real_max_size,
   but assumed to be of the same size, possibly causing memory access
   beyond the allocated area.
 * bits in tag_map between max_deptn and real_max_depth were
   initialized to 1's, making the tags permanently reserved.

In an attempt to fix above two bugs, I had removed allocation optimization
in init_tag_map and real_max_size.  Tag map/index were allocated and freed
immediately during resize.

Unfortunately, I wasn't considering that tag map/index can be resized
dynamically with tags beyond new_depth active.  This led to accessing
freed area after shrinking tags and led to the following bug reporting
thread on linux-scsi.

To fix the problem, I've revived real_max_depth without allocation
optimization in init_tag_map, and Andrew Vasquez confirmed that the
problem was fixed.  As Jens is not going to be available for a week, he
asked me to make sure that this patch reaches you.

Also, a comment was added to make sure that real_max_size is needed for
dynamic shrinking.
Signed-off-by: default avatarTejun Heo <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent c7546f8f
......@@ -719,7 +719,7 @@ struct request *blk_queue_find_tag(request_queue_t *q, int tag)
struct blk_queue_tag *bqt = q->queue_tags;
if (unlikely(bqt == NULL || tag >= bqt->max_depth))
if (unlikely(bqt == NULL || tag >= bqt->real_max_depth))
return NULL;
return bqt->tag_index[tag];
......@@ -798,6 +798,7 @@ init_tag_map(request_queue_t *q, struct blk_queue_tag *tags, int depth)
memset(tag_index, 0, depth * sizeof(struct request *));
memset(tag_map, 0, nr_ulongs * sizeof(unsigned long));
tags->real_max_depth = depth;
tags->max_depth = depth;
tags->tag_index = tag_index;
tags->tag_map = tag_map;
......@@ -871,12 +872,23 @@ int blk_queue_resize_tags(request_queue_t *q, int new_depth)
if (!bqt)
return -ENXIO;
* if we already have large enough real_max_depth. just
* adjust max_depth. *NOTE* as requests with tag value
* between new_depth and real_max_depth can be in-flight, tag
* map can not be shrunk blindly here.
if (new_depth <= bqt->real_max_depth) {
bqt->max_depth = new_depth;
return 0;
* save the old state info, so we can copy it back
tag_index = bqt->tag_index;
tag_map = bqt->tag_map;
max_depth = bqt->max_depth;
max_depth = bqt->real_max_depth;
if (init_tag_map(q, bqt, new_depth))
return -ENOMEM;
......@@ -913,7 +925,7 @@ void blk_queue_end_tag(request_queue_t *q, struct request *rq)
BUG_ON(tag == -1);
if (unlikely(tag >= bqt->max_depth))
if (unlikely(tag >= bqt->real_max_depth))
* This can happen after tag depth has been reduced.
* FIXME: how about a warning or info message here?
......@@ -301,6 +301,7 @@ struct blk_queue_tag {
struct list_head busy_list; /* fifo list of busy tags */
int busy; /* current depth */
int max_depth; /* what we will send to device */
int real_max_depth; /* what the array can hold */
atomic_t refcnt; /* map can be shared */
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