From b298d289c79211508f11cb50749b0d1d54eb244a Mon Sep 17 00:00:00 2001 From: "Srivatsa S. Bhat" Date: Fri, 9 Dec 2011 23:36:36 +0100 Subject: PM / Sleep: Fix freezer failures due to racy usermodehelper_is_disabled() Commit a144c6a (PM: Print a warning if firmware is requested when tasks are frozen) introduced usermodehelper_is_disabled() to warn and exit immediately if firmware is requested when usermodehelpers are disabled. However, it is racy. Consider the following scenario, currently used in drivers/base/firmware_class.c: ... if (usermodehelper_is_disabled()) goto out; /* Do actual work */ ... out: return err; Nothing prevents someone from disabling usermodehelpers just after the check in the 'if' condition, which means that it is quite possible to try doing the "actual work" with usermodehelpers disabled, leading to undesirable consequences. In particular, this race condition in _request_firmware() causes task freezing failures whenever suspend/hibernation is in progress because, it wrongly waits to get the firmware/microcode image from userspace when actually the usermodehelpers are disabled or userspace has been frozen. Some of the example scenarios that cause freezing failures due to this race are those that depend on userspace via request_firmware(), such as x86 microcode module initialization and microcode image reload. Previous discussions about this issue can be found at: http://thread.gmane.org/gmane.linux.kernel/1198291/focus=1200591 This patch adds proper synchronization to fix this issue. It is to be noted that this patchset fixes the freezing failures but doesn't remove the warnings. IOW, it does not attempt to add explicit synchronization to x86 microcode driver to avoid requesting microcode image at inopportune moments. Because, the warnings were introduced to highlight such cases, in the first place. And we need not silence the warnings, since we take care of the *real* problem (freezing failure) and hence, after that, the warnings are pretty harmless anyway. Signed-off-by: Srivatsa S. Bhat Signed-off-by: Rafael J. Wysocki --- drivers/base/firmware_class.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'drivers/base/firmware_class.c') diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c index 06ed6b4e7df5..d5585da14c8a 100644 --- a/drivers/base/firmware_class.c +++ b/drivers/base/firmware_class.c @@ -534,6 +534,8 @@ static int _request_firmware(const struct firmware **firmware_p, return 0; } + read_lock_usermodehelper(); + if (WARN_ON(usermodehelper_is_disabled())) { dev_err(device, "firmware: %s will not be loaded\n", name); retval = -EBUSY; @@ -572,6 +574,8 @@ static int _request_firmware(const struct firmware **firmware_p, fw_destroy_instance(fw_priv); out: + read_unlock_usermodehelper(); + if (retval) { release_firmware(firmware); *firmware_p = NULL; -- cgit v1.2.1