On Tue, Jul 16, 2019 at 12:32:53PM -0400, Daniel Jordan wrote:
> Testing padata with the tcrypt module on a 5.2 kernel...
>
> # modprobe tcrypt alg="pcrypt(rfc4106(gcm(aes)))" type=3
> # modprobe tcrypt mode=211 sec=1
>
> ...produces this splat:
>
> INFO: task modprobe:10075 blocked for more than 120 seconds.
> Not tainted 5.2.0-base+ #16
> modprobe D 0 10075 10064 0x80004080
> Call Trace:
> ? __schedule+0x4dd/0x610
> ? ring_buffer_unlock_commit+0x23/0x100
> schedule+0x6c/0x90
> schedule_timeout+0x3b/0x320
> ? trace_buffer_unlock_commit_regs+0x4f/0x1f0
> wait_for_common+0x160/0x1a0
> ? wake_up_q+0x80/0x80
> { crypto_wait_req } # entries in braces added by hand
> { do_one_aead_op }
> { test_aead_jiffies }
> test_aead_speed.constprop.17+0x681/0xf30 [tcrypt]
> do_test+0x4053/0x6a2b [tcrypt]
> ? 0xffffffffa00f4000
> tcrypt_mod_init+0x50/0x1000 [tcrypt]
> ...
>
> The second modprobe command never finishes because in padata_reorder,
> CPU0's load of reorder_objects is executed before the unlocking store in
> spin_unlock_bh(pd->lock), causing CPU0 to miss CPU1's increment:
>
> CPU0 CPU1
>
> padata_reorder padata_do_serial
> LOAD reorder_objects // 0
> INC reorder_objects // 1
> padata_reorder
> TRYLOCK pd->lock // failed
> UNLOCK pd->lock
>
> CPU0 deletes the timer before returning from padata_reorder and since no
> other job is submitted to padata, modprobe waits indefinitely.
>
> Add a pair of full barriers to guarantee proper ordering:
>
> CPU0 CPU1
>
> padata_reorder padata_do_serial
> UNLOCK pd->lock
> smp_mb()
> LOAD reorder_objects
> INC reorder_objects
> smp_mb__after_atomic()
> padata_reorder
> TRYLOCK pd->lock
>
> smp_mb__after_atomic is needed so the read part of the trylock operation
> comes after the INC, as Andrea points out. Thanks also to Andrea for
> help with writing a litmus test.
>
> Fixes: 16295bec6398 ("padata: Generic parallelization/serialization interface")
> Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> Cc: Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
> Cc: linux-arch@xxxxxxxxxxxxxxx
> Cc: linux-crypto@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
> kernel/padata.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
Patch applied. Thanks.
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
