libnvdimm, btt: fix uninitialized err_lock

When a sector mode namespace is initially created, the arena's err_lock
is not initialized.  If, on the other hand, the namespace already
exists, the mutex is initialized.  To fix the issue, I moved the mutex
initialization into the arena_alloc, which is called by both
discover_arenas and create_arenas.

This was discovered on an older kernel where mutex_trylock checks the
count to determine whether the lock is held.  Because the data structure
is kzalloc-d, that count was 0 (held), and I/O to the device would hang
forever waiting for the lock to be released (see btt_write_pg, for
example).  Current kernels have a different mutex implementation that
checks for a non-null owner, and so this doesn't show up as a problem.
If that lock were ever contended, it might cause issues, but you'd have
to be really unlucky, I think.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
index e949e3302af4743472ac26c68e9f4d54a27bb11a..5860f99113c67abf0dff3d666d5c287ef69413b7 100644 (file)
--- a/drivers/nvdimm/btt.c
+++ b/drivers/nvdimm/btt.c
@@ -630,6 +630,7 @@ static struct arena_info *alloc_arena(struct btt *btt, size_t size,
                return NULL;
        arena->nd_btt = btt->nd_btt;
        arena->sector_size = btt->sector_size;
+       mutex_init(&arena->err_lock);
 
        if (!size)
                return arena;
@@ -758,7 +759,6 @@ static int discover_arenas(struct btt *btt)
                arena->external_lba_start = cur_nlba;
                parse_arena_meta(arena, super, cur_off);
 
-               mutex_init(&arena->err_lock);
                ret = btt_freelist_init(arena);
                if (ret)
                        goto out;