Messages in this thread Patch in this message | | | From | Daniel Wagner <> | Subject | [PATCH v5 1/5] firmware: document user mode helper lock usage | Date | Fri, 9 Sep 2016 14:12:20 +0200 |
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From: Daniel Wagner <daniel.wagner@bmw-carit.de>
The lock is also used to generate warnings when a direct firmware load is requested too early.
The usermodehelper locking code was added by b298d289c792 ("PM / Sleep: Fix freezer failures due to racy usermodehelper_is_disabled()").
As Luis points out:
"Reviewing commit 247bc03742545 ("PM / Sleep: Mitigate race between the freezer and request_firmware()") which originally extended umh state machine from just being enabled/disabled, with the concepts of UMH_ENABLED, UMH_FREEZING, UMH_DISABLED -- its goal was to prevent UMH uses during suspend. So -- the "UMH lock" on firmware was actually added to help avoid races between freezing and request_firmware(). We should not re-use UMH status notifiers when the firmware UMH is disabled for the same concepts -- if we needed such a concept then we should take this out from UMH code and generalize it."
After some discussion with Ming it was decided to put a comment to the code to document the usage of the umh and a TODO to resolve this by having some generic means to detect ongoing freezing operations.
Cc: Ming Lei <ming.lei@canonical.com> Cc: Luis R. Rodriguez <mcgrof@kernel.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de> --- drivers/base/firmware_class.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c index 960f8f7..8eba1fb 100644 --- a/drivers/base/firmware_class.c +++ b/drivers/base/firmware_class.c @@ -1150,6 +1150,19 @@ _request_firmware(const struct firmware **firmware_p, const char *name, if (ret <= 0) /* error or already assigned */ goto out; + /* + * The usermode helper lock is taken to serialize the firmware + * loading even when no usermoder mode helper is used at all. + * + * Some drivers may not benefit from firmware loading cache + * when requesting loading in .resume(). In the situation of + * suspend vs. resume, it is still too early for direct + * loading. With UMH lock, we can get a warning or avoid the + * issue. + * + * TODO: Taking the UMH lock is a bit missleading and it makes + * sense to generalize this to a common freezer check. + */ ret = 0; timeout = firmware_loading_timeout(); if (opt_flags & FW_OPT_NOWAIT) { -- 2.7.4
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