On Mon, 3 Dec 2012 20:42:56 -0500
Ed Cashin <ecas...@coraid.com> wrote:
> This change avoids a race that could result in a NULL pointer
> derference following a WARNing from kobject_add_internal, "don't
> try to register things with the same name in the same directory."
>
> The problem was found with a test that forgets and discovers an
> aoe device in a loop:
>
> while test ! -r /tmp/stop; do
> aoe-flush -a
> aoe-discover
> done
>
> The race was between aoedev_flush taking aoedevs out of the
> devlist, allowing a new discovery of the same AoE target to take
> place before the driver gets around to calling
> sysfs_remove_group. Fixing that one revealed another race
> between do_open and add_disk, and this patch avoids that, too.
>
> The fix required some care, because for flushing (forgetting) an
> aoedev, some of the steps must be performed under lock and some
> must be able to sleep. Also, for discovering a new aoedev, some
> steps might sleep.
>
> The check for a bad aoedev pointer remains from a time when about
> half of this patch was done, and it was possible for the
> bdev->bd_disk->private_data to become corrupted. The check
> should be removed eventually, but it is not expected to add
> significant overhead, occurring in the aoeblk_open routine.
>
>
> ...
>
> --- a/drivers/block/aoe/aoeblk.c
> +++ b/drivers/block/aoe/aoeblk.c
> @@ -147,9 +147,18 @@ aoeblk_open(struct block_device *bdev, fmode_t mode)
> struct aoedev *d = bdev->bd_disk->private_data;
> ulong flags;
>
> + if (!virt_addr_valid(d)) {
> + pr_crit("aoe: invalid device pointer in %s\n",
> + __func__);
> + WARN_ON(1);
> + return -ENODEV;
> + }
Can this ever happen?
> + if (!(d->flags & DEVFL_UP) || d->flags & DEVFL_TKILL)
> + return -ENODEV;
> +
> mutex_lock(&aoeblk_mutex);
> spin_lock_irqsave(&d->lock, flags);
> - if (d->flags & DEVFL_UP) {
> + if (d->flags & DEVFL_UP && !(d->flags & DEVFL_TKILL)) {
> d->nopen++;
> spin_unlock_irqrestore(&d->lock, flags);
> mutex_unlock(&aoeblk_mutex);
> @@ -259,6 +268,18 @@ aoeblk_gdalloc(void *vp)
> struct request_queue *q;
> enum { KB = 1024, MB = KB * KB, READ_AHEAD = 2 * MB, };
> ulong flags;
> + int late = 0;
> +
> + spin_lock_irqsave(&d->lock, flags);
> + if (d->flags & DEVFL_GDALLOC
> + && !(d->flags & DEVFL_TKILL)
> + && !(d->flags & DEVFL_GD_NOW))
That's pretty sickly-looking code layout.
We often do
if ((d->flags & (DEVFL_GDALLOC|DEVFL_TKILL|DEVFL_GD_NOW)) ==
DEVFL_GDALLOC)
in these cases.
> + d->flags |= DEVFL_GD_NOW;
> + else
> + late = 1;
> + spin_unlock_irqrestore(&d->lock, flags);
> + if (late)
> + return;
>
> gd = alloc_disk(AOE_PARTITIONS);
> if (gd == NULL) {
>
> ...
>
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