From: Sergey Senozhatsky senozhatsky@chromium.org
[ Upstream commit dc89997264de565999a1cb55db3f295d3a8e457b ]
Always use crypto_has_comp() so that crypto can lookup module, call usermodhelper to load the modules, wait for usermodhelper to finish and so on. Otherwise crypto will do all of these steps under CPU hot-plug lock and this looks like too much stuff to handle under the CPU hot-plug lock. Besides this can end up in a deadlock when usermodhelper triggers a code path that attempts to lock the CPU hot-plug lock, that zram already holds.
An example of such deadlock:
- path A. zram grabs CPU hot-plug lock, execs /sbin/modprobe from crypto and waits for modprobe to finish
disksize_store zcomp_create __cpuhp_state_add_instance __cpuhp_state_add_instance_cpuslocked zcomp_cpu_up_prepare crypto_alloc_base crypto_alg_mod_lookup call_usermodehelper_exec wait_for_completion_killable do_wait_for_common schedule
- path B. async work kthread that brings in scsi device. It wants to register CPUHP states at some point, and it needs the CPU hot-plug lock for that, which is owned by zram.
async_run_entry_fn scsi_probe_and_add_lun scsi_mq_alloc_queue blk_mq_init_queue blk_mq_init_allocated_queue blk_mq_realloc_hw_ctxs __cpuhp_state_add_instance __cpuhp_state_add_instance_cpuslocked mutex_lock schedule
- path C. modprobe sleeps, waiting for all aync works to finish.
load_module do_init_module async_synchronize_full async_synchronize_cookie_domain schedule
[senozhatsky@chromium.org: add comment] Link: https://lkml.kernel.org/r/20220624060606.1014474-1-senozhatsky@chromium.org Link: https://lkml.kernel.org/r/20220622023501.517125-1-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky senozhatsky@chromium.org Cc: Minchan Kim minchan@kernel.org Cc: Nitin Gupta ngupta@vflare.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/zram/zcomp.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c index 33e3b76c4fa9..b08650417bf0 100644 --- a/drivers/block/zram/zcomp.c +++ b/drivers/block/zram/zcomp.c @@ -61,12 +61,6 @@ static int zcomp_strm_init(struct zcomp_strm *zstrm, struct zcomp *comp)
bool zcomp_available_algorithm(const char *comp) { - int i; - - i = sysfs_match_string(backends, comp); - if (i >= 0) - return true; - /* * Crypto does not ignore a trailing new line symbol, * so make sure you don't supply a string containing @@ -215,6 +209,11 @@ struct zcomp *zcomp_create(const char *compress) struct zcomp *comp; int error;
+ /* + * Crypto API will execute /sbin/modprobe if the compression module + * is not loaded yet. We must do it here, otherwise we are about to + * call /sbin/modprobe under CPU hot-plug lock. + */ if (!zcomp_available_algorithm(compress)) return ERR_PTR(-EINVAL);