similar to: mutex

On (Tue) 09 Sep 2014 [23:23:07], Amos Kong wrote: > (Resend to fix the subject) > > Hi Amit, Rusty > > RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1127062 > steps: > - Read random data by 'dd if=/dev/hwrng of=/dev/null' in guest > - check sysfs files in the same time, 'cat /sys/class/misc/hw_random/rng_*' > > Result: cat process will get

On (Tue) 09 Sep 2014 [23:23:07], Amos Kong wrote: > (Resend to fix the subject) > > Hi Amit, Rusty > > RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1127062 > steps: > - Read random data by 'dd if=/dev/hwrng of=/dev/null' in guest > - check sysfs files in the same time, 'cat /sys/class/misc/hw_random/rng_*' > > Result: cat process will get

On Thu, Sep 18, 2014 at 08:37:44PM +0800, Amos Kong wrote: > From: Rusty Russell <rusty at rustcorp.com.au> > > current_rng holds one reference, and we bump it every time we want > to do a read from it. > > This means we only hold the rng_mutex to grab or drop a reference, > so accessing /sys/devices/virtual/misc/hw_random/rng_current doesn't > block on read of

On Thu, Sep 18, 2014 at 08:37:44PM +0800, Amos Kong wrote: > From: Rusty Russell <rusty at rustcorp.com.au> > > current_rng holds one reference, and we bump it every time we want > to do a read from it. > > This means we only hold the rng_mutex to grab or drop a reference, > so accessing /sys/devices/virtual/misc/hw_random/rng_current doesn't > block on read of

If we read hwrng by long-running dd process, it takes too much cpu time. When we check hwrng attributes from sysfs by cat, it gets stuck. The problem can only be reproduced with non-smp guest with slow backend. This patchset changed hwrng core to always delay 10 jiffies, cat process have chance to execute protected code, the problem is resolved. Thanks. Amos Kong (2): virtio-rng cleanup: move

If we read hwrng by long-running dd process, it takes too much cpu time. When we check hwrng attributes from sysfs by cat, it gets stuck. The problem can only be reproduced with non-smp guest with slow backend. This patchset changed hwrng core to always delay 10 jiffies, cat process have chance to execute protected code, the problem is resolved. Thanks. Amos Kong (2): virtio-rng cleanup: move

There's currently a big lock around everything, and it means that we can't query sysfs (eg /sys/devices/virtual/misc/hw_random/rng_current) while the rng is reading. This is a real problem when the rng is slow, or blocked (eg. virtio_rng with qemu's default /dev/random backend) This doesn't help (it leaves the current lock untouched), just adds a lock to protect the read function

(Resend to fix the subject) Hi Amit, Rusty RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1127062 steps: - Read random data by 'dd if=/dev/hwrng of=/dev/null' in guest - check sysfs files in the same time, 'cat /sys/class/misc/hw_random/rng_*' Result: cat process will get stuck, it will return if we kill dd process. We have some static variables (eg, current_rng, data_avail,

On Tue, 16 Sep 2014 00:02:27 +0800 Amos Kong <akong at redhat.com> wrote: > It doesn't save too much cpu time as expected, just a cleanup. > > Signed-off-by: Amos Kong <akong at redhat.com> > --- > drivers/char/hw_random/core.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/char/hw_random/core.c

On Tue, 16 Sep 2014 00:02:27 +0800 Amos Kong <akong at redhat.com> wrote: > It doesn't save too much cpu time as expected, just a cleanup. > > Signed-off-by: Amos Kong <akong at redhat.com> > --- > drivers/char/hw_random/core.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/char/hw_random/core.c

If we read hwrng by long-running dd process, it takes too much cpu time and almost hold the mutex lock. When we check hwrng attributes from sysfs by cat, it gets stuck in waiting the lock releaseing. The problem can only be reproduced with non-smp guest with slow backend. This patchset resolves the issue by changing rng_dev_read() to always schedule 10 jiffies after release mutex lock, then cat

If we read hwrng by long-running dd process, it takes too much cpu time and almost hold the mutex lock. When we check hwrng attributes from sysfs by cat, it gets stuck in waiting the lock releaseing. The problem can only be reproduced with non-smp guest with slow backend. This patchset resolves the issue by changing rng_dev_read() to always schedule 10 jiffies after release mutex lock, then cat

On Wed, Sep 10, 2014 at 11:22:12AM +0530, Amit Shah wrote: > On (Tue) 09 Sep 2014 [23:23:07], Amos Kong wrote: > > (Resend to fix the subject) > > > > Hi Amit, Rusty > > > > RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1127062 > > steps: > > - Read random data by 'dd if=/dev/hwrng of=/dev/null' in guest > > - check sysfs files in

Amos Kong <akong at redhat.com> writes: > I started a QEMU (non-smp) guest with one virtio-rng device, and read > random data from /dev/hwrng by dd: > > # dd if=/dev/hwrng of=/dev/null & > > In the same time, if I check hwrng attributes from sysfs by cat: > > # cat /sys/class/misc/hw_random/rng_* > > The cat process always gets stuck with slow backend (5

Amos Kong <akong at redhat.com> writes: > I started a QEMU (non-smp) guest with one virtio-rng device, and read > random data from /dev/hwrng by dd: > > # dd if=/dev/hwrng of=/dev/null & > > In the same time, if I check hwrng attributes from sysfs by cat: > > # cat /sys/class/misc/hw_random/rng_* > > The cat process always gets stuck with slow backend (5

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My original was pain, Rusty posted a real fix. This patchset fixed two issue in v1, and tested by my 6+ cases. | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: |

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My original was pain, Rusty posted a real fix. This patchset fixed two issue in v1, and tested by my 6+ cases. | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: |

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My hotplug tests: | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: | guest) # dd if=/dev/random of=/dev/null & | hotunplug rng device from qemu monitor | | test

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My hotplug tests: | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: | guest) # dd if=/dev/random of=/dev/null & | hotunplug rng device from qemu monitor | | test

When I hotunplug a busy virtio-rng device or try to access hwrng attributes in non-smp guest, it gets stuck. My hotplug tests: | test 0: | hotunplug rng device from qemu monitor | | test 1: | guest) # dd if=/dev/hwrng of=/dev/null & | hotunplug rng device from qemu monitor | | test 2: | guest) # dd if=/dev/random of=/dev/null & | hotunplug rng device from qemu monitor | | test