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authorRafael J. Wysocki <rjw@sisk.pl>2007-07-17 07:03:35 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-17 13:23:02 -0400
commit831441862956fffa17b9801db37e6ea1650b0f69 (patch)
treeb0334921341f8f1734bdd3243de76d676329d21c /Documentation/power/swsusp.txt
parent787d2214c19bcc9b6ac48af0ce098277a801eded (diff)
Freezer: make kernel threads nonfreezable by default
Currently, the freezer treats all tasks as freezable, except for the kernel threads that explicitly set the PF_NOFREEZE flag for themselves. This approach is problematic, since it requires every kernel thread to either set PF_NOFREEZE explicitly, or call try_to_freeze(), even if it doesn't care for the freezing of tasks at all. It seems better to only require the kernel threads that want to or need to be frozen to use some freezer-related code and to remove any freezer-related code from the other (nonfreezable) kernel threads, which is done in this patch. The patch causes all kernel threads to be nonfreezable by default (ie. to have PF_NOFREEZE set by default) and introduces the set_freezable() function that should be called by the freezable kernel threads in order to unset PF_NOFREEZE. It also makes all of the currently freezable kernel threads call set_freezable(), so it shouldn't cause any (intentional) change of behaviour to appear. Additionally, it updates documentation to describe the freezing of tasks more accurately. [akpm@linux-foundation.org: build fixes] Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> Acked-by: Nigel Cunningham <nigel@nigel.suspend2.net> Cc: Pavel Machek <pavel@ucw.cz> Cc: Oleg Nesterov <oleg@tv-sign.ru> Cc: Gautham R Shenoy <ego@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/power/swsusp.txt')
-rw-r--r--Documentation/power/swsusp.txt18
1 files changed, 4 insertions, 14 deletions
diff --git a/Documentation/power/swsusp.txt b/Documentation/power/swsusp.txt
index 152b510d1bbb..aea7e9209667 100644
--- a/Documentation/power/swsusp.txt
+++ b/Documentation/power/swsusp.txt
@@ -140,21 +140,11 @@ should be sent to the mailing list available through the suspend2
140website, and not to the Linux Kernel Mailing List. We are working 140website, and not to the Linux Kernel Mailing List. We are working
141toward merging suspend2 into the mainline kernel. 141toward merging suspend2 into the mainline kernel.
142 142
143Q: A kernel thread must voluntarily freeze itself (call 'refrigerator'). 143Q: What is the freezing of tasks and why are we using it?
144I found some kernel threads that don't do it, and they don't freeze
145so the system can't sleep. Is this a known behavior?
146
147A: All such kernel threads need to be fixed, one by one. Select the
148place where the thread is safe to be frozen (no kernel semaphores
149should be held at that point and it must be safe to sleep there), and
150add:
151
152 try_to_freeze();
153
154If the thread is needed for writing the image to storage, you should
155instead set the PF_NOFREEZE process flag when creating the thread (and
156be very careful).
157 144
145A: The freezing of tasks is a mechanism by which user space processes and some
146kernel threads are controlled during hibernation or system-wide suspend (on some
147architectures). See freezing-of-tasks.txt for details.
158 148
159Q: What is the difference between "platform" and "shutdown"? 149Q: What is the difference between "platform" and "shutdown"?
160 150