Sergey Senozhatsky 2504102938 zram: do not lookup algorithm in backends table ... [ Upstream commit dc89997264 ] 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>		2022-08-25 11:40:34 +02:00
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Kconfig	zram: break the strict dependency from lzo	2020-12-15 12:13:47 -08:00
Makefile	treewide: Add SPDX license identifier - Makefile/Kconfig	2019-05-21 10:50:46 +02:00
zcomp.c	zram: do not lookup algorithm in backends table	2022-08-25 11:40:34 +02:00
zcomp.h	zram: Use local lock to protect per-CPU data	2020-05-28 10:31:10 +02:00
zram_drv.c	zram: off by one in read_block_state()	2021-11-18 19:17:10 +01:00
zram_drv.h	Merge branch 'akpm' (patches from Andrew)	2021-07-02 12:08:10 -07:00