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Sergey Senozhatsky dc89997264 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>

2022-07-03 18:08:50 -07:00

aoe

aoe: Avoid flush_scheduled_work() usage

2022-05-01 06:41:41 -06:00

drbd

drbd: Return true/false (not 1/0) from bool functions

2022-04-17 19:54:24 -06:00

mtip32xx

mtip32xx: fix typo in comment

2022-05-21 06:32:27 -06:00

null_blk

block: null_blk: Fix null_zone_write()