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...text. > > > > I don't understand this explanation? I'd expect the sysfs process to be > > woken by the mutex_unlock(). > > But actually sysfs process's not woken always, this is they the > process gets stuck. %s/they/why/ Hi Rusty, Reference: http://www.linuxgrill.com/anonymous/fire/netfilter/kernel-hacking-HOWTO-2.html read() syscall of /dev/hwrng will enter into kernel, the read operation is rng_dev_read(), it's userspace context (not interrupt context). Userspace context doesn't allow other user contexts run on that CPU, unless the kernel code...

...text. > > > > I don't understand this explanation? I'd expect the sysfs process to be > > woken by the mutex_unlock(). > > But actually sysfs process's not woken always, this is they the > process gets stuck. %s/they/why/ Hi Rusty, Reference: http://www.linuxgrill.com/anonymous/fire/netfilter/kernel-hacking-HOWTO-2.html read() syscall of /dev/hwrng will enter into kernel, the read operation is rng_dev_read(), it's userspace context (not interrupt context). Userspace context doesn't allow other user contexts run on that CPU, unless the kernel code...

Amos Kong <akong at redhat.com> writes: > When I check hwrng attributes in sysfs, cat process always gets > stuck if guest has only 1 vcpu and uses a slow rng backend. > > Currently we check if there is any tasks waiting to be run on > current cpu in rng_dev_read() by need_resched(). But need_resched() > doesn't work because rng_dev_read() is executing in user context.

Amos Kong <akong at redhat.com> writes: > When I check hwrng attributes in sysfs, cat process always gets > stuck if guest has only 1 vcpu and uses a slow rng backend. > > Currently we check if there is any tasks waiting to be run on > current cpu in rng_dev_read() by need_resched(). But need_resched() > doesn't work because rng_dev_read() is executing in user context.