3.2.99-rc1 review patch. If anyone has any objections, please let me know.
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From: Waiman Long longman@redhat.com
commit 5acb3cc2c2e9d3020a4fee43763c6463767f1572 upstream.
The lockdep code had reported the following unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(s_active#228); lock(&bdev->bd_mutex/1); lock(s_active#228); lock(&bdev->bd_mutex);
*** DEADLOCK ***
The deadlock may happen when one task (CPU1) is trying to delete a partition in a block device and another task (CPU0) is accessing tracing sysfs file (e.g. /sys/block/dm-1/trace/act_mask) in that partition.
The s_active isn't an actual lock. It is a reference count (kn->count) on the sysfs (kernfs) file. Removal of a sysfs file, however, require a wait until all the references are gone. The reference count is treated like a rwsem using lockdep instrumentation code.
The fact that a thread is in the sysfs callback method or in the ioctl call means there is a reference to the opended sysfs or device file. That should prevent the underlying block structure from being removed.
Instead of using bd_mutex in the block_device structure, a new blk_trace_mutex is now added to the request_queue structure to protect access to the blk_trace structure.
Suggested-by: Christoph Hellwig hch@infradead.org Signed-off-by: Waiman Long longman@redhat.com Acked-by: Steven Rostedt (VMware) rostedt@goodmis.org
Fix typo in patch subject line, and prune a comment detailing how the code used to work.
Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Ben Hutchings ben@decadent.org.uk --- block/blk-core.c | 3 +++ include/linux/blkdev.h | 1 + kernel/trace/blktrace.c | 18 ++++++++++++------ 3 files changed, 16 insertions(+), 6 deletions(-)
--- a/block/blk-core.c +++ b/block/blk-core.c @@ -499,6 +499,9 @@ struct request_queue *blk_alloc_queue_no
kobject_init(&q->kobj, &blk_queue_ktype);
+#ifdef CONFIG_BLK_DEV_IO_TRACE + mutex_init(&q->blk_trace_mutex); +#endif mutex_init(&q->sysfs_lock); spin_lock_init(&q->__queue_lock);
--- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -361,6 +361,7 @@ struct request_queue { int node; #ifdef CONFIG_BLK_DEV_IO_TRACE struct blk_trace *blk_trace; + struct mutex blk_trace_mutex; #endif /* * for flush operations --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -631,6 +631,12 @@ int blk_trace_startstop(struct request_q } EXPORT_SYMBOL_GPL(blk_trace_startstop);
+/* + * When reading or writing the blktrace sysfs files, the references to the + * opened sysfs or device files should prevent the underlying block device + * from being removed. So no further delete protection is really needed. + */ + /** * blk_trace_ioctl: - handle the ioctls associated with tracing * @bdev: the block device @@ -648,7 +654,7 @@ int blk_trace_ioctl(struct block_device if (!q) return -ENXIO;
- mutex_lock(&bdev->bd_mutex); + mutex_lock(&q->blk_trace_mutex);
switch (cmd) { case BLKTRACESETUP: @@ -674,7 +680,7 @@ int blk_trace_ioctl(struct block_device break; }
- mutex_unlock(&bdev->bd_mutex); + mutex_unlock(&q->blk_trace_mutex); return ret; }
@@ -1660,7 +1666,7 @@ static ssize_t sysfs_blk_trace_attr_show if (q == NULL) goto out_bdput;
- mutex_lock(&bdev->bd_mutex); + mutex_lock(&q->blk_trace_mutex);
if (attr == &dev_attr_enable) { ret = sprintf(buf, "%u\n", !!q->blk_trace); @@ -1679,7 +1685,7 @@ static ssize_t sysfs_blk_trace_attr_show ret = sprintf(buf, "%llu\n", q->blk_trace->end_lba);
out_unlock_bdev: - mutex_unlock(&bdev->bd_mutex); + mutex_unlock(&q->blk_trace_mutex); out_bdput: bdput(bdev); out: @@ -1721,7 +1727,7 @@ static ssize_t sysfs_blk_trace_attr_stor if (q == NULL) goto out_bdput;
- mutex_lock(&bdev->bd_mutex); + mutex_lock(&q->blk_trace_mutex);
if (attr == &dev_attr_enable) { if (value) @@ -1747,7 +1753,7 @@ static ssize_t sysfs_blk_trace_attr_stor }
out_unlock_bdev: - mutex_unlock(&bdev->bd_mutex); + mutex_unlock(&q->blk_trace_mutex); out_bdput: bdput(bdev); out: