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    Subject[PATCH AUTOSEL 4.9 054/141] padata: always acquire cpu_hotplug_lock before pinst->lock
    Date
    From: Daniel Jordan <daniel.m.jordan@oracle.com>

    [ Upstream commit 38228e8848cd7dd86ccb90406af32de0cad24be3 ]

    lockdep complains when padata's paths to update cpumasks via CPU hotplug
    and sysfs are both taken:

    # echo 0 > /sys/devices/system/cpu/cpu1/online
    # echo ff > /sys/kernel/pcrypt/pencrypt/parallel_cpumask

    ======================================================
    WARNING: possible circular locking dependency detected
    5.4.0-rc8-padata-cpuhp-v3+ #1 Not tainted
    ------------------------------------------------------
    bash/205 is trying to acquire lock:
    ffffffff8286bcd0 (cpu_hotplug_lock.rw_sem){++++}, at: padata_set_cpumask+0x2b/0x120

    but task is already holding lock:
    ffff8880001abfa0 (&pinst->lock){+.+.}, at: padata_set_cpumask+0x26/0x120

    which lock already depends on the new lock.

    padata doesn't take cpu_hotplug_lock and pinst->lock in a consistent
    order. Which should be first? CPU hotplug calls into padata with
    cpu_hotplug_lock already held, so it should have priority.

    Fixes: 6751fb3c0e0c ("padata: Use get_online_cpus/put_online_cpus")
    Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
    Cc: Eric Biggers <ebiggers@kernel.org>
    Cc: Herbert Xu <herbert@gondor.apana.org.au>
    Cc: Steffen Klassert <steffen.klassert@secunet.com>
    Cc: linux-crypto@vger.kernel.org
    Cc: linux-kernel@vger.kernel.org
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/padata.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/kernel/padata.c b/kernel/padata.c
    index 63449fc584daf..ee5da2394cf57 100644
    --- a/kernel/padata.c
    +++ b/kernel/padata.c
    @@ -635,8 +635,8 @@ int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
    struct cpumask *serial_mask, *parallel_mask;
    int err = -EINVAL;

    - mutex_lock(&pinst->lock);
    get_online_cpus();
    + mutex_lock(&pinst->lock);

    switch (cpumask_type) {
    case PADATA_CPU_PARALLEL:
    @@ -654,8 +654,8 @@ int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
    err = __padata_set_cpumasks(pinst, parallel_mask, serial_mask);

    out:
    - put_online_cpus();
    mutex_unlock(&pinst->lock);
    + put_online_cpus();

    return err;
    }
    --
    2.20.1
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