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authorSergey Senozhatsky <senozhatsky@chromium.org>2022-06-22 05:35:01 +0300
committerakpm <akpm@linux-foundation.org>2022-07-04 04:08:50 +0300
commitdc89997264de565999a1cb55db3f295d3a8e457b (patch)
tree334f2f3700632a06e73642819c4591dd80dcf573 /drivers
parente8da368a1e42a8056d1a6b419e1b91b6cf11d77e (diff)
downloadlinux-dc89997264de565999a1cb55db3f295d3a8e457b.tar.xz
zram: do not lookup algorithm in backends table
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>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/block/zram/zcomp.c11
1 files changed, 5 insertions, 6 deletions
diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 052aa3f65514..0916de952e09 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -63,12 +63,6 @@ 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
@@ -217,6 +211,11 @@ 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);