Andrew Morton wrote: > On Fri, 16 Mar 2007 17:16:39 +0000 Paulo Marques wrote: > >> Does freeze_processes() / unfreeze_processes() solve this by only >> freezing processes that have voluntarily scheduled (opposed to just >> being preempted)? > > It goes much much further than that. Those processes need to actually > perform an explicit call to try_to_freeze(). Ok, I've just done a few tests with the attached patch. It basically creates a freeze_machine_run function that is equivalent in interface to stop_machine_run, but uses freeze_processes / thaw_processes to stop the machine. This is more of a proof of concept than an actual patch. At the very least "freeze_machine_run" should be moved to kernel/power/process.c and declared at include/linux/freezer.h so that it could be treated as a more general purpose function and not something that is module specific. Anyway, I then tested it by running a modprobe/rmmod loop while running a "cat /proc/kallsyms" loop. On the first run I forgot to remove the mutex_lock(module_mutex) from the /proc/kallsyms read path and the freezer was unable to freeze the "cat" process that was waiting for the same mutex that the freezer process was holding :P After removing the module_mutex locking from "module_get_kallsym" everything was going fine (at least I got no oopses) until I got this: kernel: Stopping user space processes timed out after 20 seconds (1 tasks refusing to freeze): kernel: kbluetoothd kernel: Restarting tasks ... <4> Strange, kseriod not stopped kernel: Strange, pdflush not stopped kernel: Strange, pdflush not stopped kernel: Strange, kswapd0 not stopped kernel: Strange, cifsoplockd not stopped kernel: Strange, cifsdnotifyd not stopped kernel: Strange, jfsIO not stopped kernel: Strange, jfsCommit not stopped kernel: Strange, jfsCommit not stopped kernel: Strange, jfsSync not stopped kernel: Strange, xfslogd/0 not stopped kernel: Strange, xfslogd/1 not stopped kernel: Strange, xfsdatad/0 not stopped kernel: Strange, xfsdatad/1 not stopped kernel: Strange, kjournald not stopped kernel: Strange, khubd not stopped kernel: Strange, khelper not stopped kernel: Strange, kbluetoothd not stopped kernel: done. I repeated the test and did a Alt+SysRq+T to try to find out what kbluetoothd was doing and got this: kernel: kbluetoothd D 79A11860 0 19156 1 19142 (NOTLB) kernel: 9a269e4c 00000082 00000001 79a11860 00000000 79a09860 c7018030 00000003 kernel: 9a269e71 78475100 c7ebe000 c6730e40 00000000 00000001 00000001 00000001 kernel: 00000000 9a2d7570 79a11860 c7018140 00000000 00001832 42430d03 000000ab kernel: Call Trace: kernel: [<7845dba3>] wait_for_completion+0x7d/0xb7 kernel: [<781190ba>] default_wake_function+0x0/0xc kernel: [<781190ba>] default_wake_function+0x0/0xc kernel: [<7812c759>] call_usermodehelper_keys+0xd1/0xf1 kernel: [<7812c41e>] request_module+0x96/0xd9 kernel: [<783e30fe>] sock_alloc_inode+0x20/0x4e kernel: [<78172559>] alloc_inode+0x15/0x115 kernel: [<78172d87>] new_inode+0x24/0x81 kernel: [<783e4003>] __sock_create+0x111/0x199 kernel: [<783e40a3>] sock_create+0x18/0x1d kernel: [<783e40e1>] sys_socket+0x1c/0x43 kernel: [<783e51da>] sys_socketcall+0x247/0x24c kernel: [<78121b2d>] sys_gettimeofday+0x2c/0x65 kernel: [<78103f10>] sysenter_past_esp+0x5d/0x81 And this was as far as I got... This actually seems like a better approach than to hold module_mutex everywhere to account for an operation that should be "rare" (module loading/unloading). If something like this goes in, there are probably a few more places inside module.c where we can drop the locking completely. However, it still has a few gotchas. Apart from the problem above (which may still be me doing something wrong) it makes module loading / unloading depend on CONFIG_PM which is somewhat unexpected for the user. Would it make sense to separate the process freezing / thawing API from actual power management and create a new config option (CONFIG_FREEZER?) that was automatically selected by the systems that used it (CONFIG_PM, CONFIG_MODULES, etc.)? or is that overkill? -- Paulo Marques - www.grupopie.com "Nostalgia isn't what it used to be."