[PATCH 6/9] bcon: add a release work struct

From: Joern Engel
Date: Thu Feb 28 2013 - 18:05:10 EST

The final bcon_put() can be called from atomic context, by way of
bio_endio(). In that case we would sleep in invalidate_mapping_pages(),
with the usual unhappy results.

In nearly a year of production use, I have only seen a matching
backtrace once. There was a second known issue that could be reproduced
by "yes h > /proc/sysrq-trigger" and concurrently pulling and replugging
the blockconsole device. It took be somewhere around 30 pulls and sore
thumbs to reproduce and I never found the time to get to the bottom of
it. Quite likely the two issues are identical.

Signed-off-by: Joern Engel <joern@xxxxxxxxx>
drivers/block/blockconsole.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/block/blockconsole.c b/drivers/block/blockconsole.c
index 32f6c62..b4730f8 100644
--- a/drivers/block/blockconsole.c
+++ b/drivers/block/blockconsole.c
@@ -65,6 +65,7 @@ struct blockconsole {
struct block_device *bdev;
struct console console;
struct work_struct unregister_work;
+ struct work_struct release_work;
struct task_struct *writeback_thread;
struct notifier_block panic_block;
@@ -74,9 +75,10 @@ static void bcon_get(struct blockconsole *bc)

-static void bcon_release(struct kref *kref)
+static void __bcon_release(struct work_struct *work)
- struct blockconsole *bc = container_of(kref, struct blockconsole, kref);
+ struct blockconsole *bc = container_of(work, struct blockconsole,
+ release_work);

__free_pages(bc->zero_page, 0);
__free_pages(bc->pages, 8);
@@ -85,6 +87,14 @@ static void bcon_release(struct kref *kref)

+static void bcon_release(struct kref *kref)
+ struct blockconsole *bc = container_of(kref, struct blockconsole, kref);
+ /* bcon_release can be called from atomic context */
+ schedule_work(&bc->release_work);
static void bcon_put(struct blockconsole *bc)
kref_put(&bc->kref, bcon_release);
@@ -512,6 +522,7 @@ static int bcon_create(const char *devname)
if (IS_ERR(bc->writeback_thread))
goto out2;
INIT_WORK(&bc->unregister_work, bcon_unregister);
+ INIT_WORK(&bc->release_work, __bcon_release);
bc->panic_block.notifier_call = blockconsole_panic;
bc->panic_block.priority = INT_MAX;

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