5.4-stable review patch. If anyone has any objections, please let me know.
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From: Hsin-Te Yuan yuanhsinte@chromium.org
[ Upstream commit 1a4aabc27e95674837f2e25f4ef340c0469e6203 ]
According to POSIX spec, EAGAIN returned by read with O_NONBLOCK set means the read would block. Hence, the common implementation in nonblocking model will poll the file when the nonblocking read returns EAGAIN. However, when the target file is thermal zone, this mechanism will totally malfunction because thermal zone doesn't implement sysfs notification and thus the poll will never return.
For example, the read in Golang implemnts such method and sometimes hangs at reading some thermal zones via sysfs.
Change to return -ENODATA instead of -EAGAIN to userspace.
Signed-off-by: Hsin-Te Yuan yuanhsinte@chromium.org Link: https://patch.msgid.link/20250620-temp-v3-1-6becc6aeb66c@chromium.org Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/thermal/thermal_sysfs.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c index 17b2361bc8f2..fc768b61f483 100644 --- a/drivers/thermal/thermal_sysfs.c +++ b/drivers/thermal/thermal_sysfs.c @@ -39,10 +39,13 @@ temp_show(struct device *dev, struct device_attribute *attr, char *buf)
ret = thermal_zone_get_temp(tz, &temperature);
- if (ret) - return ret; + if (!ret) + return sprintf(buf, "%d\n", temperature);
- return sprintf(buf, "%d\n", temperature); + if (ret == -EAGAIN) + return -ENODATA; + + return ret; }
static ssize_t