projects / linux-2.6-block.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)); | |
| 3e1d1d28 | 15 | try_to_freeze(); |
| 1da177e4 LT |
16 | } while (!signal_pending(current)); |
| 17 | ||
| 18 | from drivers/usb/core/hub.c::hub_thread() | |
| 19 | ||
| 20 | ||
| 21 | The Unfreezable | |
| 22 | ||
| 23 | Some kernel threads however, must not be frozen. The kernel must | |
| 24 | be able to finish pending IO operations and later on be able to | |
| 25 | write the memory image to disk. Kernel threads needed to do IO | |
| 26 | must stay awake. Such threads must mark themselves unfreezable | |
| 27 | like this: | |
| 28 | ||
| 29 | /* | |
| 30 | * This thread doesn't need any user-level access, | |
| 31 | * so get rid of all our resources. | |
| 32 | */ | |
| 33 | daemonize("usb-storage"); | |
| 34 | ||
| 35 | current->flags |= PF_NOFREEZE; | |
| 36 | ||
| 37 | from drivers/usb/storage/usb.c::usb_stor_control_thread() | |
| 38 | ||
| 39 | Such drivers are themselves responsible for staying quiet during | |
| 40 | the actual snapshotting. |