From 521f7288a8126a8ec28e3ab623aacf0590684b80 Mon Sep 17 00:00:00 2001 From: Anton Vorontsov Date: Sat, 26 May 2012 06:20:29 -0700 Subject: [PATCH] pstore/platform: Disable automatic updates by default Having automatic updates seems pointless for production system, 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. Maybe for non-oops message types it would make sense to re-enable 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. So, let's disable the updates by default. [1] BUG: unable to handle kernel paging request at fffffffffffffff8 IP: [] kthread_data+0xb/0x20 [...] Process kworker/0:1 (pid: 14, threadinfo ffff8800072c0000, task ffff88000725b100) [... Call Trace: [] wq_worker_sleeping+0x10/0xa0 [] __schedule+0x568/0x7d0 [] ? trace_hardirqs_on+0xd/0x10 [] ? call_rcu_sched+0x12/0x20 [] ? release_task+0x156/0x2d0 [] ? release_task+0x1e/0x2d0 [] ? trace_hardirqs_on+0xd/0x10 [] schedule+0x24/0x70 [] do_exit+0x1f8/0x370 [] oops_end+0x77/0xb0 [] no_context+0x1a6/0x1b5 [] __bad_area_nosemaphore+0x1ce/0x1ed [] ? ttwu_queue+0xc6/0xe0 [] bad_area_nosemaphore+0xe/0x10 [] do_page_fault+0x2c7/0x450 [] ? __lock_release+0x6b/0xe0 [] ? mark_held_locks+0x61/0x140 [] ? __wake_up+0x4e/0x70 [] ? trace_hardirqs_off_thunk+0x3a/0x3c [] ? pstore_register+0x120/0x120 [] page_fault+0x1f/0x30 [] ? pstore_register+0x120/0x120 [] ? memcpy+0x68/0x110 [] ? pstore_get_records+0x3a/0x130 [] ? persistent_ram_copy_old+0x64/0x90 [] ramoops_pstore_read+0x84/0x130 [] pstore_get_records+0x79/0x130 [] ? process_one_work+0x116/0x450 [] ? pstore_register+0x120/0x120 [] pstore_dowork+0xe/0x10 [] process_one_work+0x174/0x450 [] ? process_one_work+0x116/0x450 [] worker_thread+0x123/0x2d0 [] ? manage_workers.isra.28+0x120/0x120 [] kthread+0x8e/0xa0 [] kernel_thread_helper+0x4/0x10 [] ? retint_restore_args+0xe/0xe [] ? __init_kthread_worker+0x70/0x70 [] ? 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 [] kthread_data+0xb/0x20 RSP CR2: fffffffffffffff8 ---[ end trace 996a332dc399111d ]--- Fixing recursive fault but reboot is needed! Signed-off-by: Anton Vorontsov Signed-off-by: Greg Kroah-Hartman --- fs/pstore/platform.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c index 34ca3141eb0a..be4614f24a2f 100644 --- a/fs/pstore/platform.c +++ b/fs/pstore/platform.c @@ -41,10 +41,12 @@ * whether the system is actually still running well enough * to let someone see the entry */ -static int pstore_update_ms = 60000; +static int pstore_update_ms = -1; module_param_named(update_ms, pstore_update_ms, int, 0600); MODULE_PARM_DESC(update_ms, "milliseconds before pstore updates its content " - "(default is 60000; -1 means runtime updates are disabled)"); + "(default is -1, which means runtime updates are disabled; " + "enabling this option is not safe, it may lead to further " + "corruption on Oopses)"); static int pstore_new_entry; -- 2.34.1