[Xen-devel] [PATCH 02/16] blkfront: fixes for 'xm block-detach ... --force'

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Jan Beulich <jbeulich@xxxxxxxxxx>

Prevent prematurely freeing 'struct blkfront_info' instances (when the
xenbus data structures are gone, but the Linux ones are still needed).

Prevent adding a disk with the same (major, minor) [and hence the same
name and sysfs entries, which leads to oopses] when the previous
instance wasn't fully de-allocated yet.

This still doesn't address all issues resulting from forced detach:
I/O submitted after the detach still blocks forever, likely preventing
subsequent un-mounting from completing. It's not clear to me (not
knowing much about the block layer) how this can be avoided.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 drivers/block/xen-blkfront.c |   83 +++++++++++++++++++++++++++++++++++++++---
 1 files changed, 78 insertions(+), 5 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 6839947..b1b16e5 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -104,6 +104,10 @@ struct blkfront_info
 
 static DEFINE_SPINLOCK(blkif_io_lock);
 
+static unsigned int nr_minors;
+static unsigned long *minors;
+static DEFINE_SPINLOCK(minor_lock);
+
 #define MAXIMUM_OUTSTANDING_BLOCK_REQS \
        (BLKIF_MAX_SEGMENTS_PER_REQUEST * BLK_RING_SIZE)
 #define GRANT_INVALID_REF      0
@@ -138,6 +142,55 @@ static void add_id_to_freelist(struct blkfront_info *info,
        info->shadow_free = id;
 }
 
+static int xlbd_reserve_minors(unsigned int minor, unsigned int nr)
+{
+       unsigned int end = minor + nr;
+       int rc;
+
+       if (end > nr_minors) {
+               unsigned long *bitmap, *old;
+
+               bitmap = kzalloc(BITS_TO_LONGS(end) * sizeof(*bitmap),
+                                GFP_KERNEL);
+               if (bitmap == NULL)
+                       return -ENOMEM;
+
+               spin_lock(&minor_lock);
+               if (end > nr_minors) {
+                       old = minors;
+                       memcpy(bitmap, minors,
+                              BITS_TO_LONGS(nr_minors) * sizeof(*bitmap));
+                       minors = bitmap;
+                       nr_minors = BITS_TO_LONGS(end) * BITS_PER_LONG;
+               } else
+                       old = bitmap;
+               spin_unlock(&minor_lock);
+               kfree(old);
+       }
+
+       spin_lock(&minor_lock);
+       if (find_next_bit(minors, end, minor) >= end) {
+               for (; minor < end; ++minor)
+                       __set_bit(minor, minors);
+               rc = 0;
+       } else
+               rc = -EBUSY;
+       spin_unlock(&minor_lock);
+
+       return rc;
+}
+
+static void xlbd_release_minors(unsigned int minor, unsigned int nr)
+{
+       unsigned int end = minor + nr;
+
+       BUG_ON(end > nr_minors);
+       spin_lock(&minor_lock);
+       for (; minor < end; ++minor)
+               __clear_bit(minor, minors);
+       spin_unlock(&minor_lock);
+}
+
 static void blkif_restart_queue_callback(void *arg)
 {
        struct blkfront_info *info = (struct blkfront_info *)arg;
@@ -417,9 +470,14 @@ static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
        if ((minor % nr_parts) == 0)
                nr_minors = nr_parts;
 
+       err = xlbd_reserve_minors(minor, nr_minors);
+       if (err)
+               goto out;
+       err = -ENODEV;
+
        gd = alloc_disk(nr_minors);
        if (gd == NULL)
-               goto out;
+               goto release;
 
        offset = minor / nr_parts;
 
@@ -450,7 +508,7 @@ static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
 
        if (xlvbd_init_blk_queue(gd, sector_size)) {
                del_gendisk(gd);
-               goto out;
+               goto release;
        }
 
        info->rq = gd->queue;
@@ -470,6 +528,8 @@ static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
 
        return 0;
 
+ release:
+       xlbd_release_minors(minor, nr_minors);
  out:
        return err;
 }
@@ -924,6 +984,7 @@ static void blkfront_connect(struct blkfront_info *info)
 static void blkfront_closing(struct xenbus_device *dev)
 {
        struct blkfront_info *info = dev_get_drvdata(&dev->dev);
+       unsigned int minor, nr_minors;
        unsigned long flags;
 
        dev_dbg(&dev->dev, "blkfront_closing: %s removed\n", dev->nodename);
@@ -946,7 +1007,10 @@ static void blkfront_closing(struct xenbus_device *dev)
        blk_cleanup_queue(info->rq);
        info->rq = NULL;
 
+       minor = info->gd->first_minor;
+       nr_minors = info->gd->minors;
        del_gendisk(info->gd);
+       xlbd_release_minors(minor, nr_minors);
 
  out:
        xenbus_frontend_closed(dev);
@@ -1004,7 +1068,10 @@ static int blkfront_remove(struct xenbus_device *dev)
 
        blkif_free(info, 0);
 
-       kfree(info);
+       if(info->users == 0)
+               kfree(info);
+       else
+               info->is_ready = -1;
 
        return 0;
 }
@@ -1013,12 +1080,15 @@ static int blkfront_is_ready(struct xenbus_device *dev)
 {
        struct blkfront_info *info = dev_get_drvdata(&dev->dev);
 
-       return info->is_ready;
+       return info->is_ready > 0;
 }
 
 static int blkif_open(struct block_device *bdev, fmode_t mode)
 {
        struct blkfront_info *info = bdev->bd_disk->private_data;
+
+       if(info->is_ready < 0)
+               return -ENODEV;
        info->users++;
        return 0;
 }
@@ -1034,7 +1104,10 @@ static int blkif_release(struct gendisk *disk, fmode_t 
mode)
                struct xenbus_device *dev = info->xbdev;
                enum xenbus_state state = 
xenbus_read_driver_state(dev->otherend);
 
-               if (state == XenbusStateClosing && info->is_ready)
+               if(info->is_ready < 0) {
+                       blkfront_closing(dev);
+                       kfree(info);
+               } else if (state == XenbusStateClosing && info->is_ready)
                        blkfront_closing(dev);
        }
        return 0;
-- 
1.7.1.1


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