From: Alasdair G Kergon upgrade_mode() sets bdev to NULL temporarily, and does not have any locking to exclude anything from seeing that NULL. In dm_table_any_congested() bdev_get_queue() can dereference that NULL and cause a reported oops. Fix this by not changing that field during the mode upgrade. Cc: stable@kernel.org Cc: Neil Brown Signed-off-by: Alasdair G Kergon --- drivers/md/dm-table.c | 26 ++++++++++++++------------ 1 files changed, 14 insertions(+), 12 deletions(-) Index: linux-2.6.29/drivers/md/dm-table.c =================================================================== --- linux-2.6.29.orig/drivers/md/dm-table.c 2009-04-02 16:34:52.000000000 +0100 +++ linux-2.6.29/drivers/md/dm-table.c 2009-04-02 16:45:40.000000000 +0100 @@ -399,28 +399,30 @@ static int check_device_area(struct dm_d } /* - * This upgrades the mode on an already open dm_dev. Being + * This upgrades the mode on an already open dm_dev, being * careful to leave things as they were if we fail to reopen the - * device. + * device and not to touch the existing bdev field in case + * it is accessed concurrently inside dm_table_any_congested(). */ static int upgrade_mode(struct dm_dev_internal *dd, fmode_t new_mode, struct mapped_device *md) { int r; - struct dm_dev_internal dd_copy; - dev_t dev = dd->dm_dev.bdev->bd_dev; + struct dm_dev_internal dd_new, dd_old; - dd_copy = *dd; + dd_new = dd_old = *dd; + + dd_new.dm_dev.mode |= new_mode; + dd_new.dm_dev.bdev = NULL; + + r = open_dev(&dd_new, dd->dm_dev.bdev->bd_dev, md); + if (r) + return r; dd->dm_dev.mode |= new_mode; - dd->dm_dev.bdev = NULL; - r = open_dev(dd, dev, md); - if (!r) - close_dev(&dd_copy, md); - else - *dd = dd_copy; + close_dev(&dd_old, md); - return r; + return 0; } /*