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SubjectRe: bsg locking patches update
From
On Mon, 26 May 2008 12:53:18 -0400
Pete Wyckoff <pw@osc.edu> wrote:

> I finally got around to testing the set of lifetime management
> fixes you applied. This is 2.6.26-rc3 with some varlen, bidi,
> iser patches, and iovec on bsg, but nothing that should affect
> the locking.
>
> I can confirm that the first two of these three old bugs are
> no longer reproducable:
>
> http://marc.info/?l=linux-scsi&m=120508166505141&w=2
> http://marc.info/?l=linux-scsi&m=120508177905365&w=2
> http://marc.info/?l=linux-scsi&m=120508178005376&w=2
>
> Thanks! The third, however, is a hang that still can happen. But
> it is very obscure and requires a bit of timing to get right. As a
> reminder, here's the setup, and updated traces.

Ah, sorry about it. I didn't understand the third correctly.


> Maybe it is necessary to split up that bsg_mutex to use multiple
> finer-grained locks.

We could but we use bsg_mutex to protect bsg_device_list and idr. So I
think that we don't need hold bsg_mutex during
bsg_complete_all_commands. How about this?


diff --git a/block/bsg.c b/block/bsg.c
index f0b7cd3..d81104e 100644
--- a/block/bsg.c
+++ b/block/bsg.c
@@ -721,8 +721,6 @@ static int bsg_put_device(struct bsg_device *bd)
int ret = 0, do_free;
struct request_queue *q = bd->queue;

- mutex_lock(&bsg_mutex);
-
do_free = atomic_dec_and_test(&bd->ref_count);
if (!do_free)
goto out;
@@ -741,10 +739,12 @@ static int bsg_put_device(struct bsg_device *bd)
*/
ret = bsg_complete_all_commands(bd);

+ mutex_lock(&bsg_mutex);
hlist_del(&bd->dev_list);
+ mutex_unlock(&bsg_mutex);
+
kfree(bd);
out:
- mutex_unlock(&bsg_mutex);
kref_put(&q->bsg_dev.ref, bsg_kref_release_function);
if (do_free)
blk_put_queue(q);
--
1.5.4.2


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