| Message ID | 20190329163011.7370-1-lvivier@redhat.com (mailing list archive) |
|---|---|
| State | Rejected |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | hwrng: core - don't block in add_early_randomness() | expand |
On Fri, Mar 29, 2019 at 05:30:11PM +0100, Laurent Vivier wrote: > If the device is not ready to provide data the kernel will > be stuck indefinitely in the init function. > > This is not a problem if the device is driven using a module, > but if the driver is linked directly into the kernel then the > kernel boot sequence hangs. > > This can happen with virtio-rng device with rng-egd backend > with no data provider, for instance with QEMU command line parameters: > > ... > -chardev socket,id=charrng0,host=localhost,port=2345,server,nowait \ > -object rng-egd,id=objrng0,chardev=charrng0 \ > -device virtio-rng-pci,rng=objrng0,id=rng0 > > To avoid that, we can call rng_get_data() in non blocking mode because > the function already manages the case where byte_read is > 0 (if the device is not already initialized). > > See also commit d3cc7996473a > ("hwrng: fetch randomness only after device init") > > Signed-off-by: Laurent Vivier <lvivier@redhat.com> I think this is either not a bug (make sure that the user supplies a RNG source) or it should be addressed in virtio-rng. Cheers,
On 08/04/2019 08:31, Herbert Xu wrote: > On Fri, Mar 29, 2019 at 05:30:11PM +0100, Laurent Vivier wrote: >> If the device is not ready to provide data the kernel will >> be stuck indefinitely in the init function. >> >> This is not a problem if the device is driven using a module, >> but if the driver is linked directly into the kernel then the >> kernel boot sequence hangs. >> >> This can happen with virtio-rng device with rng-egd backend >> with no data provider, for instance with QEMU command line parameters: >> >> ... >> -chardev socket,id=charrng0,host=localhost,port=2345,server,nowait \ >> -object rng-egd,id=objrng0,chardev=charrng0 \ >> -device virtio-rng-pci,rng=objrng0,id=rng0 >> >> To avoid that, we can call rng_get_data() in non blocking mode because >> the function already manages the case where byte_read is >> 0 (if the device is not already initialized). >> >> See also commit d3cc7996473a >> ("hwrng: fetch randomness only after device init") >> >> Signed-off-by: Laurent Vivier <lvivier@redhat.com> > > I think this is either not a bug (make sure that the user supplies > a RNG source) or it should be addressed in virtio-rng. Yes, I did more investigation and I agree. Thanks, Laurent
diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 95be7228f327..3866d6b8017c 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -67,7 +67,7 @@ static void add_early_randomness(struct hwrng *rng) size_t size = min_t(size_t, 16, rng_buffer_size()); mutex_lock(&reading_mutex); - bytes_read = rng_get_data(rng, rng_buffer, size, 1); + bytes_read = rng_get_data(rng, rng_buffer, size, 0); mutex_unlock(&reading_mutex); if (bytes_read > 0) add_device_randomness(rng_buffer, bytes_read);
If the device is not ready to provide data the kernel will be stuck indefinitely in the init function. This is not a problem if the device is driven using a module, but if the driver is linked directly into the kernel then the kernel boot sequence hangs. This can happen with virtio-rng device with rng-egd backend with no data provider, for instance with QEMU command line parameters: ... -chardev socket,id=charrng0,host=localhost,port=2345,server,nowait \ -object rng-egd,id=objrng0,chardev=charrng0 \ -device virtio-rng-pci,rng=objrng0,id=rng0 To avoid that, we can call rng_get_data() in non blocking mode because the function already manages the case where byte_read is 0 (if the device is not already initialized). See also commit d3cc7996473a ("hwrng: fetch randomness only after device init") Signed-off-by: Laurent Vivier <lvivier@redhat.com> --- drivers/char/hw_random/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)