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zram: do not lookup algorithm in backends table

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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>
This commit is contained in:
Sergey Senozhatsky 2022-06-22 11:35:01 +09:00 committed by akpm
parent e8da368a1e
commit dc89997264
1 changed files with 5 additions and 6 deletions
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11
drivers/block/zram/zcomp.c
View File

@ -63,12 +63,6 @@ static int zcomp_strm_init(struct zcomp_strm *zstrm, struct zcomp *comp)
bool zcomp_available_algorithm(const char *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, * Crypto does not ignore a trailing new line symbol,
* so make sure you don't supply a string containing * so make sure you don't supply a string containing
@ -217,6 +211,11 @@ struct zcomp *zcomp_create(const char *compress)
struct zcomp *comp; struct zcomp *comp;
int error; 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)) if (!zcomp_available_algorithm(compress))
return ERR_PTR(-EINVAL); return ERR_PTR(-EINVAL);