(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, etc) in hw_random/core.c, they are protected by rng_mutex. I try to workaround this issue by undelay(100) after mutex_unlock() in rng_dev_read(). This gives chance for hwrng_attr_*_show() to get mutex. This patch also contains some cleanup, moving some code out of mutex protection. Do you have some suggestion? Thanks. diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index aa30a25..fa69020 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -194,6 +194,7 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf, } mutex_unlock(&rng_mutex); + udelay(100); if (need_resched()) schedule_timeout_interruptible(1); @@ -233,10 +234,10 @@ static ssize_t hwrng_attr_current_store(struct device *dev, int err; struct hwrng *rng; + err = -ENODEV; err = mutex_lock_interruptible(&rng_mutex); if (err) return -ERESTARTSYS; - err = -ENODEV; list_for_each_entry(rng, &rng_list, list) { if (strcmp(rng->name, buf) == 0) { if (rng == current_rng) { @@ -270,8 +271,8 @@ static ssize_t hwrng_attr_current_show(struct device *dev, return -ERESTARTSYS; if (current_rng) name = current_rng->name; - ret = snprintf(buf, PAGE_SIZE, "%s\n", name); mutex_unlock(&rng_mutex); + ret = snprintf(buf, PAGE_SIZE, "%s\n", name); return ret; } @@ -284,19 +285,19 @@ static ssize_t hwrng_attr_available_show(struct device *dev, ssize_t ret = 0; struct hwrng *rng; + buf[0] = '\0'; err = mutex_lock_interruptible(&rng_mutex); if (err) return -ERESTARTSYS; - buf[0] = '\0'; list_for_each_entry(rng, &rng_list, list) { strncat(buf, rng->name, PAGE_SIZE - ret - 1); ret += strlen(rng->name); strncat(buf, " ", PAGE_SIZE - ret - 1); ret++; } + mutex_unlock(&rng_mutex); strncat(buf, "\n", PAGE_SIZE - ret - 1); ret++; - mutex_unlock(&rng_mutex); return ret; } -- Amos. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
