Having automatic updates seems pointless, and even dangerous and thus counter-productive:
1. If we can mount pstore, or read files, we can as well read /proc/kmsg. So, there's little point in duplicating the functionality and present the same information but via another userland ABI;
2. Expecting the kernel to behave sanely after oops/panic is naive. It might work, but you'd rather not try it. Screwed up kernel can do rather bad things, like recursive faults[1]; and pstore rather provoking bad things to happen. It uses:
1. Timers (assumes sane interrupts state); 2. Workqueues and mutexes (assumes scheduler in a sane state); 3. kzalloc (a working slab allocator);
That's too much for a dead kernel, so the debugging facility itself might just make debugging harder, which is not what we want.
So, let's remove the automatic updates, this keeps things simple and safe.
(Maybe for non-oops message types it would make sense to add automatic updates, but so far I don't see any use case for this. Even for tracing, it has its own run-time/normal ABI, so we're only interested in pstore upon next boot, to retrieve what has gone wrong with HW or SW.)
[1] BUG: unable to handle kernel paging request at fffffffffffffff8 IP: [<ffffffff8104801b>] kthread_data+0xb/0x20 [...] Process kworker/0:1 (pid: 14, threadinfo ffff8800072c0000, task ffff88000725b100) [... Call Trace: [<ffffffff81043710>] wq_worker_sleeping+0x10/0xa0 [<ffffffff813687a8>] __schedule+0x568/0x7d0 [<ffffffff8106c24d>] ? trace_hardirqs_on+0xd/0x10 [<ffffffff81087e22>] ? call_rcu_sched+0x12/0x20 [<ffffffff8102b596>] ? release_task+0x156/0x2d0 [<ffffffff8102b45e>] ? release_task+0x1e/0x2d0 [<ffffffff8106c24d>] ? trace_hardirqs_on+0xd/0x10 [<ffffffff81368ac4>] schedule+0x24/0x70 [<ffffffff8102cba8>] do_exit+0x1f8/0x370 [<ffffffff810051e7>] oops_end+0x77/0xb0 [<ffffffff8135c301>] no_context+0x1a6/0x1b5 [<ffffffff8135c4de>] __bad_area_nosemaphore+0x1ce/0x1ed [<ffffffff81053156>] ? ttwu_queue+0xc6/0xe0 [<ffffffff8135c50b>] bad_area_nosemaphore+0xe/0x10 [<ffffffff8101fa47>] do_page_fault+0x2c7/0x450 [<ffffffff8106e34b>] ? __lock_release+0x6b/0xe0 [<ffffffff8106bf21>] ? mark_held_locks+0x61/0x140 [<ffffffff810502fe>] ? __wake_up+0x4e/0x70 [<ffffffff81185f7d>] ? trace_hardirqs_off_thunk+0x3a/0x3c [<ffffffff81158970>] ? pstore_register+0x120/0x120 [<ffffffff8136a37f>] page_fault+0x1f/0x30 [<ffffffff81158970>] ? pstore_register+0x120/0x120 [<ffffffff81185ab8>] ? memcpy+0x68/0x110 [<ffffffff8115875a>] ? pstore_get_records+0x3a/0x130 [<ffffffff811590f4>] ? persistent_ram_copy_old+0x64/0x90 [<ffffffff81158bf4>] ramoops_pstore_read+0x84/0x130 [<ffffffff81158799>] pstore_get_records+0x79/0x130 [<ffffffff81042536>] ? process_one_work+0x116/0x450 [<ffffffff81158970>] ? pstore_register+0x120/0x120 [<ffffffff8115897e>] pstore_dowork+0xe/0x10 [<ffffffff81042594>] process_one_work+0x174/0x450 [<ffffffff81042536>] ? process_one_work+0x116/0x450 [<ffffffff81042e13>] worker_thread+0x123/0x2d0 [<ffffffff81042cf0>] ? manage_workers.isra.28+0x120/0x120 [<ffffffff81047d8e>] kthread+0x8e/0xa0 [<ffffffff8136ba74>] kernel_thread_helper+0x4/0x10 [<ffffffff8136a199>] ? retint_restore_args+0xe/0xe [<ffffffff81047d00>] ? __init_kthread_worker+0x70/0x70 [<ffffffff8136ba70>] ? gs_change+0xb/0xb Code: be e2 00 00 00 48 c7 c7 d1 2a 4e 81 e8 bf fb fd ff 48 8b 5d f0 4c 8b 65 f8 c9 c3 0f 1f 44 00 00 48 8b 87 08 02 00 00 55 48 89 e5 <48> 8b 40 f8 5d c3 66 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 RIP [<ffffffff8104801b>] kthread_data+0xb/0x20 RSP <ffff8800072c1888> CR2: fffffffffffffff8 ---[ end trace 996a332dc399111d ]--- Fixing recursive fault but reboot is needed!
Signed-off-by: Anton Vorontsov anton.vorontsov@linaro.org --- fs/pstore/platform.c | 37 ------------------------------------- 1 file changed, 37 deletions(-)
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c index a3f6d96..3c7ac9b 100644 --- a/fs/pstore/platform.c +++ b/fs/pstore/platform.c @@ -27,30 +27,13 @@ #include <linux/module.h> #include <linux/pstore.h> #include <linux/string.h> -#include <linux/timer.h> #include <linux/slab.h> #include <linux/uaccess.h> #include <linux/hardirq.h> -#include <linux/workqueue.h>
#include "internal.h"
/* - * We defer making "oops" entries appear in pstore - see - * whether the system is actually still running well enough - * to let someone see the entry - */ -#define PSTORE_INTERVAL (60 * HZ) - -static int pstore_new_entry; - -static void pstore_timefunc(unsigned long); -static DEFINE_TIMER(pstore_timer, pstore_timefunc, 0, 0); - -static void pstore_dowork(struct work_struct *); -static DECLARE_WORK(pstore_work, pstore_dowork); - -/* * pstore_lock just protects "psinfo" during * calls to pstore_register() */ @@ -140,8 +123,6 @@ static void pstore_dump(struct kmsg_dumper *dumper,
ret = psinfo->write(PSTORE_TYPE_DMESG, reason, &id, part, hsize + l1_cpy + l2_cpy, psinfo); - if (ret == 0 && reason == KMSG_DUMP_OOPS && pstore_is_mounted()) - pstore_new_entry = 1; l1 -= l1_cpy; l2 -= l2_cpy; total += l1_cpy + l2_cpy; @@ -227,9 +208,6 @@ int pstore_register(struct pstore_info *psi) kmsg_dump_register(&pstore_dumper); pstore_register_console();
- pstore_timer.expires = jiffies + PSTORE_INTERVAL; - add_timer(&pstore_timer); - return 0; } EXPORT_SYMBOL_GPL(pstore_register); @@ -275,20 +253,5 @@ out: failed, psi->name); }
-static void pstore_dowork(struct work_struct *work) -{ - pstore_get_records(1); -} - -static void pstore_timefunc(unsigned long dummy) -{ - if (pstore_new_entry) { - pstore_new_entry = 0; - schedule_work(&pstore_work); - } - - mod_timer(&pstore_timer, jiffies + PSTORE_INTERVAL); -} - module_param(backend, charp, 0444); MODULE_PARM_DESC(backend, "Pstore backend to use");