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    Subject[PATCH 4.9 046/264] random: Use wait_event_freezable() in add_hwgenerator_randomness()
    Date
    From: Stephen Boyd <swboyd@chromium.org>

    commit 59b569480dc8bb9dce57cdff133853a842dfd805 upstream.

    Sebastian reports that after commit ff296293b353 ("random: Support freezable
    kthreads in add_hwgenerator_randomness()") we can call might_sleep() when the
    task state is TASK_INTERRUPTIBLE (state=1). This leads to the following warning.

    do not call blocking ops when !TASK_RUNNING; state=1 set at [<00000000349d1489>] prepare_to_wait_event+0x5a/0x180
    WARNING: CPU: 0 PID: 828 at kernel/sched/core.c:6741 __might_sleep+0x6f/0x80
    Modules linked in:

    CPU: 0 PID: 828 Comm: hwrng Not tainted 5.3.0-rc7-next-20190903+ #46
    RIP: 0010:__might_sleep+0x6f/0x80

    Call Trace:
    kthread_freezable_should_stop+0x1b/0x60
    add_hwgenerator_randomness+0xdd/0x130
    hwrng_fillfn+0xbf/0x120
    kthread+0x10c/0x140
    ret_from_fork+0x27/0x50

    We shouldn't call kthread_freezable_should_stop() from deep within the
    wait_event code because the task state is still set as
    TASK_INTERRUPTIBLE instead of TASK_RUNNING and
    kthread_freezable_should_stop() will try to call into the freezer with
    the task in the wrong state. Use wait_event_freezable() instead so that
    it calls schedule() in the right place and tries to enter the freezer
    when the task state is TASK_RUNNING instead.

    Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Cc: Keerthy <j-keerthy@ti.com>
    Fixes: ff296293b353 ("random: Support freezable kthreads in add_hwgenerator_randomness()")
    Signed-off-by: Stephen Boyd <swboyd@chromium.org>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/char/random.c | 12 +++++-------
    1 file changed, 5 insertions(+), 7 deletions(-)

    --- a/drivers/char/random.c
    +++ b/drivers/char/random.c
    @@ -327,6 +327,7 @@
    #include <linux/percpu.h>
    #include <linux/cryptohash.h>
    #include <linux/fips.h>
    +#include <linux/freezer.h>
    #include <linux/ptrace.h>
    #include <linux/kmemcheck.h>
    #include <linux/workqueue.h>
    @@ -2473,7 +2474,6 @@ void add_hwgenerator_randomness(const ch
    size_t entropy)
    {
    struct entropy_store *poolp = &input_pool;
    - bool frozen = false;

    if (unlikely(crng_init == 0)) {
    crng_fast_load(buffer, count);
    @@ -2484,13 +2484,11 @@ void add_hwgenerator_randomness(const ch
    * We'll be woken up again once below random_write_wakeup_thresh,
    * or when the calling thread is about to terminate.
    */
    - wait_event_interruptible(random_write_wait,
    - kthread_freezable_should_stop(&frozen) ||
    + wait_event_freezable(random_write_wait,
    + kthread_should_stop() ||
    ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);
    - if (!frozen) {
    - mix_pool_bytes(poolp, buffer, count);
    - credit_entropy_bits(poolp, entropy);
    - }
    + mix_pool_bytes(poolp, buffer, count);
    + credit_entropy_bits(poolp, entropy);
    }
    EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);


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