On Sat, Mar 21 2015 at 11:11am -0400, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Wed, Jan 14, 2015 at 4:42 AM, Christoph Hellwig <hch@xxxxxx> wrote: > > If we have dirty inodes we need to call the filesystem for it, even if the > > device has been removed and the filesystem will error out early. The > > current code does that by reassining all dirty inodes to the default > > backing_dev_info when a bdi is unlinked, but that's pretty pointless given > > that the bdi must always outlive the super block. > > > > Instead of stopping writeback at unregister time and moving inodes to the > > default bdi just keep the current bdi alive until it is destroyed. The > > containing objects of the bdi ensure this doesn't happen until all > > writeback has finished by erroring out. > > > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > > Reviewed-by: Tejun Heo <tj@xxxxxxxxxx> > > --- > > mm/backing-dev.c | 91 +++++++++++++++----------------------------------------- > > 1 file changed, 24 insertions(+), 67 deletions(-) > > Hey Christoph, > > Just a heads up: your commit c4db59d31e39ea067c32163ac961e9c80198fd37 > is suspected as the first bad commit in a bisect performed to track > down the cause of DM crashes reported in this BZ: > https://bugzilla.redhat.com/show_bug.cgi?id=1202449 > > I've yet to look closely at _why_ this commit but figured I'd share > since this appears to be a 4.0-rcX regression. FYI, here is the DM fix I've staged for 4.0-rc6. I'll continue testing the various DM targets before requesting Linus to pull. >From 63a4f065ece613b6d575b538234375b0e9c23bbc Mon Sep 17 00:00:00 2001 From: Mike Snitzer <snitzer@xxxxxxxxxx> Date: Mon, 23 Mar 2015 17:01:43 -0400 Subject: [PATCH] dm: fix add_disk() NULL pointer due to race with free_dev() Commit c4db59d31e39 ("fs: don't reassign dirty inodes to default_backing_dev_info") exposed DM to a latent race in free_dev() vs add_disk() in relation to management of the device's minor number. Fix this by refactoring free_dev() to match cleanup order of the alloc_dev() error path. Move cleanup of the gendisk, queue, and bdev to _before_ the cleanup of the idr managed minor number. Also, purely due to cleanup that fell out during the free_dev() audit: - adjust dm_blk_close() to access the gendisk's private_data under the _minor_lock spinlock. - move __dm_destroy()'s dm_get_live_table() call out from under the _minor_lock spinlock. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1202449 Reported-by: Zdenek Kabelac <zkabelac@xxxxxxxxxx> Reported-by: Jeff Moyer <jmoyer@xxxxxxxxxx> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> --- drivers/md/dm.c | 26 ++++++++++++++++---------- 1 files changed, 16 insertions(+), 10 deletions(-) diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 9b641b3..8001fe9 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -433,7 +433,6 @@ static int dm_blk_open(struct block_device *bdev, fmode_t mode) dm_get(md); atomic_inc(&md->open_count); - out: spin_unlock(&_minor_lock); @@ -442,16 +441,20 @@ out: static void dm_blk_close(struct gendisk *disk, fmode_t mode) { - struct mapped_device *md = disk->private_data; + struct mapped_device *md; spin_lock(&_minor_lock); + md = disk->private_data; + if (WARN_ON(!md)) + goto out; + if (atomic_dec_and_test(&md->open_count) && (test_bit(DMF_DEFERRED_REMOVE, &md->flags))) queue_work(deferred_remove_workqueue, &deferred_remove_work); dm_put(md); - +out: spin_unlock(&_minor_lock); } @@ -2241,7 +2244,6 @@ static void free_dev(struct mapped_device *md) int minor = MINOR(disk_devt(md->disk)); unlock_fs(md); - bdput(md->bdev); destroy_workqueue(md->wq); if (md->kworker_task) @@ -2252,19 +2254,22 @@ static void free_dev(struct mapped_device *md) mempool_destroy(md->rq_pool); if (md->bs) bioset_free(md->bs); - blk_integrity_unregister(md->disk); - del_gendisk(md->disk); + cleanup_srcu_struct(&md->io_barrier); free_table_devices(&md->table_devices); - free_minor(minor); + dm_stats_cleanup(&md->stats); spin_lock(&_minor_lock); md->disk->private_data = NULL; spin_unlock(&_minor_lock); - + if (blk_get_integrity(md->disk)) + blk_integrity_unregister(md->disk); + del_gendisk(md->disk); put_disk(md->disk); blk_cleanup_queue(md->queue); - dm_stats_cleanup(&md->stats); + bdput(md->bdev); + free_minor(minor); + module_put(THIS_MODULE); kfree(md); } @@ -2642,8 +2647,9 @@ static void __dm_destroy(struct mapped_device *md, bool wait) might_sleep(); - spin_lock(&_minor_lock); map = dm_get_live_table(md, &srcu_idx); + + spin_lock(&_minor_lock); idr_replace(&_minor_idr, MINOR_ALLOCED, MINOR(disk_devt(dm_disk(md)))); set_bit(DMF_FREEING, &md->flags); spin_unlock(&_minor_lock); -- 1.7.4.4 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
