On (25/01/30 09:08), Dan Carpenter wrote:

Commit 7ec2cb65ef0d ("zram: unlock slot during recompression") from
Jan 27, 2025 (linux-next), leads to the following Smatch static
checker warning:

	drivers/block/zram/zram_drv.c:1960 recompress_slot()
	warn: passing freed memory 'zstrm' (line 1943)

Hi Dan,
Thank you for the report.

[..]

    1923         for (; prio < prio_max; prio++) {
    1924                 if (!zram->comps[prio])
    1925                         continue;
    1926 
    1927                 num_recomps++;
    1928                 zstrm = zcomp_stream_get(zram->comps[prio]);
    1929                 src = kmap_local_page(page);
    1930                 ret = zcomp_compress(zram->comps[prio], zstrm,
    1931                                      src, &comp_len_new);
    1932                 kunmap_local(src);
    1933 
    1934                 if (ret)
    1935                         break;
    1936 
    1937                 class_index_new = zs_lookup_class_index(zram->mem_pool,
    1938                                                         comp_len_new);
    1939 
    1940                 /* Continue until we make progress */
    1941                 if (class_index_new >= class_index_old ||
    1942                     (threshold && comp_len_new >= threshold)) {
    1943                         zcomp_stream_put(zram->comps[prio], zstrm);

Imagine we hit this continue path.  The right thing is probably to set
zstrm = NULL before the continue or it might be to set ret = -EINVAL.

We still need to make sure that ZRAM_INCOMPRESSIBLE is set appropriately,
so zstrm = NULL won't do the trick.  Let me take a look.