[PATCH 0/2] fix sbitmap initialization and null_blk tagset setup

[Nilay Shroff <nilay@linux.ibm.com>]

Hi,

This patchset fixes two subtle issues discovered while unit testing 
nr_hw_queue update code using null_blk driver. 

The first patch in the series, fixes an issue in the sbitmap initialization
code, where sb->alloc_hint is not explicitly set to NULL when the sbitmap
depth is zero. This can lead to a kernel crash in sbitmap_free(), which
unconditionally calls free_percpu() on sb->alloc_hint — even if it was 
never allocated. The crash is caused by dereferencing an invalid pointer
or stale garbage value. 

The second patch in the series fixes a bug in the null_blk driver where
the driver_data field of the tagset is not properly initialized when 
setting up shared tagsets. This omission causes null_map_queues() to fail
during nr_hw_queues update, leading to no software queues (ctx) being 
mapped to new hardware queues (hctx). As a result, the affected hctx 
remains unused for any IO. Interestingly, this bug exposed the first 
issue with sbitmap freeing.

As usual, review and feedback are most welcome!

Nilay Shroff (2):
  lib/sbitmap: fix kernel crash observed when sbitmap depth is zero
  null_blk: fix set->driver_data while setting up tagset

 drivers/block/null_blk/main.c | 3 ++-
 lib/sbitmap.c                 | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

-- 
2.50.1