projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 1da177e4 LT |
1 | KERNEL THREADS |
| 2 | ||
| 3 | ||
| 4 | Freezer | |
| 5 | ||
| 6 | Upon entering a suspended state the system will freeze all | |
| 7 | tasks. This is done by delivering pseudosignals. This affects | |
| 8 | kernel threads, too. To successfully freeze a kernel thread | |
| 9 | the thread has to check for the pseudosignal and enter the | |
| 10 | refrigerator. Code to do this looks like this: | |
| 11 | ||
| 12 | do { | |
| 13 | hub_events(); | |
| 14 | wait_event_interruptible(khubd_wait, !list_empty(&hub_event_list)); | |
| 15 | if (current->flags & PF_FREEZE) | |
| 16 | refrigerator(PF_FREEZE); | |
| 17 | } while (!signal_pending(current)); | |
| 18 | ||
| 19 | from drivers/usb/core/hub.c::hub_thread() | |
| 20 | ||
| 21 | ||
| 22 | The Unfreezable | |
| 23 | ||
| 24 | Some kernel threads however, must not be frozen. The kernel must | |
| 25 | be able to finish pending IO operations and later on be able to | |
| 26 | write the memory image to disk. Kernel threads needed to do IO | |
| 27 | must stay awake. Such threads must mark themselves unfreezable | |
| 28 | like this: | |
| 29 | ||
| 30 | /* | |
| 31 | * This thread doesn't need any user-level access, | |
| 32 | * so get rid of all our resources. | |
| 33 | */ | |
| 34 | daemonize("usb-storage"); | |
| 35 | ||
| 36 | current->flags |= PF_NOFREEZE; | |
| 37 | ||
| 38 | from drivers/usb/storage/usb.c::usb_stor_control_thread() | |
| 39 | ||
| 40 | Such drivers are themselves responsible for staying quiet during | |
| 41 | the actual snapshotting. |