This is a note to let you know that I've just added the patch titled random: wake up /dev/random writers after zap to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: random-wake-up-dev-random-writers-after-zap.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 98a6339452404845edb6877242b34db902195293 Author: Jason A. Donenfeld <Jason@xxxxxxxxx> Date: Fri Jan 28 23:44:03 2022 +0100 random: wake up /dev/random writers after zap [ Upstream commit 042e293e16e3aa9794ce60c29f5b7b0c8170f933 ] When account() is called, and the amount of entropy dips below random_write_wakeup_bits, we wake up the random writers, so that they can write some more in. However, the RNDZAPENTCNT/RNDCLEARPOOL ioctl sets the entropy count to zero -- a potential reduction just like account() -- but does not unblock writers. This commit adds the missing logic to that ioctl to unblock waiting writers. Reviewed-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/char/random.c b/drivers/char/random.c index a27ae3999ff32..ebe86de9d0acc 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1963,7 +1963,10 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg) */ if (!capable(CAP_SYS_ADMIN)) return -EPERM; - input_pool.entropy_count = 0; + if (xchg(&input_pool.entropy_count, 0) && random_write_wakeup_bits) { + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); + } return 0; case RNDRESEEDCRNG: if (!capable(CAP_SYS_ADMIN))