[PATCH] bcache: prevent crash on changing writeback_running

[Stefan Bader]

commit a664d0f05a2ec02c8f042db536d84d15d6e19e81
bcache: fix crash on shutdown in passthrough mode

added a safeguard in the shutdown case. At least while not being
attached it is also possible to trigger a kernel bug by writing into
writeback_running. This change adds the same check before trying to
wake up the thread for that case.

Signed-off-by: Stefan Bader <***@canonical.com>
---
drivers/md/bcache/writeback.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
index 0a9dab1..073a042 100644
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -63,7 +63,8 @@ static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,

static inline void bch_writeback_queue(struct cached_dev *dc)
{
- wake_up_process(dc->writeback_thread);
+ if (!IS_ERR_OR_NULL(dc->writeback_thread))
+ wake_up_process(dc->writeback_thread);
}

static inline void bch_writeback_add(struct cached_dev *dc)

[Slava Pestov]

Thanks, this is now in our development branch.

On Tue, Aug 19, 2014 at 6:01 AM, Stefan Bader

Post by Stefan Bader
commit a664d0f05a2ec02c8f042db536d84d15d6e19e81
bcache: fix crash on shutdown in passthrough mode
added a safeguard in the shutdown case. At least while not being
attached it is also possible to trigger a kernel bug by writing into
writeback_running. This change adds the same check before trying to
wake up the thread for that case.
---
drivers/md/bcache/writeback.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
index 0a9dab1..073a042 100644
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -63,7 +63,8 @@ static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,
static inline void bch_writeback_queue(struct cached_dev *dc)
{
- wake_up_process(dc->writeback_thread);
+ if (!IS_ERR_OR_NULL(dc->writeback_thread))
+ wake_up_process(dc->writeback_thread);
}
static inline void bch_writeback_add(struct cached_dev *dc)
--
1.9.1
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in
More majordomo info at http://vger.kernel.org/majordomo-info.html

[Stefan Bader]

Post by Slava Pestov
Thanks, this is now in our development branch.

Thanks. :) This kind of brings up another question: how are stable patches
handled for bcache. Someone handling them centrally like for the network stack
or tagging for stable and if that missed, individual proposals?

I am asking because it looks like for all kernels between 3.13..3.16 (inclusive)
the set of

a664d0f05a2ec02c8f042db536d84d15d6e19e81
bcache: fix crash on shutdown in passthrough mode
9e5c353510b26500bd6b8309823ac9ef2837b761
bcache: fix uninterruptible sleep in writeback thread

plus the one I did would be useful. Right now I only tested with 3.13 with those
and at least avoid the lockdep warnings and crashes I saw before. I only see an
unexplainable load of 1 when idle but having one bcache device configured in a
VM (Xen or KVM). Since writeback should be fixed, maybe gc...

-Stefan

Post by Slava Pestov
On Tue, Aug 19, 2014 at 6:01 AM, Stefan Bader

Post by Stefan Bader
commit a664d0f05a2ec02c8f042db536d84d15d6e19e81
bcache: fix crash on shutdown in passthrough mode
added a safeguard in the shutdown case. At least while not being
attached it is also possible to trigger a kernel bug by writing into
writeback_running. This change adds the same check before trying to
wake up the thread for that case.
---
drivers/md/bcache/writeback.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
index 0a9dab1..073a042 100644
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -63,7 +63,8 @@ static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,
static inline void bch_writeback_queue(struct cached_dev *dc)
{
- wake_up_process(dc->writeback_thread);
+ if (!IS_ERR_OR_NULL(dc->writeback_thread))
+ wake_up_process(dc->writeback_thread);
}
static inline void bch_writeback_add(struct cached_dev *dc)
--
1.9.1
--
To unsubscribe from this list: send the line "unsubscribe linux-bcache" in
More majordomo info at http://vger.kernel.org/majordomo-info.html