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author | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 15:20:36 -0700 |
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committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 15:20:36 -0700 |
commit | 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch) | |
tree | 0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/power/kernel_threads.txt | |
download | linux-stable-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz linux-stable-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.bz2 linux-stable-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.zip |
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Diffstat (limited to 'Documentation/power/kernel_threads.txt')
-rw-r--r-- | Documentation/power/kernel_threads.txt | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/Documentation/power/kernel_threads.txt b/Documentation/power/kernel_threads.txt new file mode 100644 index 000000000000..60b548105edf --- /dev/null +++ b/Documentation/power/kernel_threads.txt @@ -0,0 +1,41 @@ +KERNEL THREADS + + +Freezer + +Upon entering a suspended state the system will freeze all +tasks. This is done by delivering pseudosignals. This affects +kernel threads, too. To successfully freeze a kernel thread +the thread has to check for the pseudosignal and enter the +refrigerator. Code to do this looks like this: + + do { + hub_events(); + wait_event_interruptible(khubd_wait, !list_empty(&hub_event_list)); + if (current->flags & PF_FREEZE) + refrigerator(PF_FREEZE); + } while (!signal_pending(current)); + +from drivers/usb/core/hub.c::hub_thread() + + +The Unfreezable + +Some kernel threads however, must not be frozen. The kernel must +be able to finish pending IO operations and later on be able to +write the memory image to disk. Kernel threads needed to do IO +must stay awake. Such threads must mark themselves unfreezable +like this: + + /* + * This thread doesn't need any user-level access, + * so get rid of all our resources. + */ + daemonize("usb-storage"); + + current->flags |= PF_NOFREEZE; + +from drivers/usb/storage/usb.c::usb_stor_control_thread() + +Such drivers are themselves responsible for staying quiet during +the actual snapshotting. |