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Currently, to tell a task that it should go to the refrigerator, we set the
PF_FREEZE flag for it and send a fake signal to it. Unfortunately there
are two SMP-related problems with this approach. First, a task running on
another CPU may be updating its flags while the freezer attempts to set
PF_FREEZE for it and this may leave the task's flags in an inconsistent
state. Second, there is a potential race between freeze_process() and
refrigerator() in which freeze_process() running on one CPU is reading a
task's PF_FREEZE flag while refrigerator() running on another CPU has just
set PF_FROZEN for the same task and attempts to reset PF_FREEZE for it. If
the refrigerator wins the race, freeze_process() will state that PF_FREEZE
hasn't been set for the task and will set it unnecessarily, so the task
will go to the refrigerator once again after it's been thawed.
To solve first of these problems we need to stop using PF_FREEZE to tell
tasks that they should go to the refrigerator. Instead, we can introduce a
special TIF_*** flag and use it for this purpose, since it is allowed to
change the other tasks' TIF_*** flags and there are special calls for it.
To avoid the freeze_process()-refrigerator() race we can make
freeze_process() to always check the task's PF_FROZEN flag after it's read
its "freeze" flag. We should also make sure that refrigerator() will
always reset the task's "freeze" flag after it's set PF_FROZEN for it.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: Andi Kleen <ak@muc.de>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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freezer.h uses task_struct fields so it should include sched.h.
CC [M] fs/jfs/jfs_txnmgr.o
In file included from fs/jfs/jfs_txnmgr.c:49:
include/linux/freezer.h: In function 'frozen':
include/linux/freezer.h:9: error: dereferencing pointer to incomplete type
include/linux/freezer.h:9: error: 'PF_FROZEN' undeclared (first use in this function)
include/linux/freezer.h:9: error: (Each undeclared identifier is reported only once
include/linux/freezer.h:9: error: for each function it appears in.)
include/linux/freezer.h: In function 'freezing':
include/linux/freezer.h:17: error: dereferencing pointer to incomplete type
include/linux/freezer.h:17: error: 'PF_FREEZE' undeclared (first use in this function)
include/linux/freezer.h: In function 'freeze':
include/linux/freezer.h:26: error: dereferencing pointer to incomplete type
include/linux/freezer.h:26: error: 'PF_FREEZE' undeclared (first use in this function)
include/linux/freezer.h: In function 'do_not_freeze':
include/linux/freezer.h:34: error: dereferencing pointer to incomplete type
include/linux/freezer.h:34: error: 'PF_FREEZE' undeclared (first use in this function)
include/linux/freezer.h: In function 'thaw_process':
include/linux/freezer.h:43: error: dereferencing pointer to incomplete type
include/linux/freezer.h:43: error: 'PF_FROZEN' undeclared (first use in this function)
include/linux/freezer.h:44: warning: implicit declaration of function 'wake_up_process'
include/linux/freezer.h: In function 'frozen_process':
include/linux/freezer.h:55: error: dereferencing pointer to incomplete type
include/linux/freezer.h:55: error: dereferencing pointer to incomplete type
include/linux/freezer.h:55: error: 'PF_FREEZE' undeclared (first use in this function)
include/linux/freezer.h:55: error: 'PF_FROZEN' undeclared (first use in this function)
fs/jfs/jfs_txnmgr.c: In function 'freezing':
include/linux/freezer.h:18: warning: control reaches end of non-void function
make[2]: *** [fs/jfs/jfs_txnmgr.o] Error 1
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Move the loop from thaw_processes() to a separate function and call it
independently for kernel threads and user space processes so that the order
of thawing tasks is clearly visible.
Drop thaw_kernel_threads() which is never used.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Nigel Cunningham <nigel@suspend2.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Modify process thawing so that we can thaw kernel space without thawing
userspace, and thaw kernelspace first. This will be useful in later
patches, where I intend to get swsusp thawing kernel threads only before
seeking to free memory.
Signed-off-by: Nigel Cunningham <nigel@suspend2.net>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Move process freezing functions from include/linux/sched.h to freezer.h, so
that modifications to the freezer or the kernel configuration don't require
recompiling just about everything.
[akpm@osdl.org: fix ueagle driver]
Signed-off-by: Nigel Cunningham <nigel@suspend2.net>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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