user/sven/linux.git/kernel/printk, branch v4.14.156

printk: Give error on attempt to set log buffer length to over 2G

2019-11-24T07:23:25Z

[ Upstream commit e6fe3e5b7d16e8f146a4ae7fe481bc6e97acde1e ] The current printk() is ready to handle log buffer size up to 2G. Give an explicit error for users who want to use larger log buffer. Also fix printk formatting to show the 2G as a positive number. Link: http://lkml.kernel.org/r/20181008135916.gg4kkmoki5bgtco5@pathway.suse.cz Cc: rostedt@goodmis.org Cc: linux-kernel@vger.kernel.org Suggested-by: Sergey Senozhatsky Signed-off-by: He Zhe Reviewed-by: Sergey Senozhatsky [pmladek: Fixed to the really safe limit 2GB.] Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

printk: Do not lose last line in kmsg buffer dump

2019-10-05T10:48:04Z

commit c9dccacfccc72c32692eedff4a27a4b0833a2afd upstream. kmsg_dump_get_buffer() is supposed to select all the youngest log messages which fit into the provided buffer. It determines the correct start index by using msg_print_text() with a NULL buffer to calculate the size of each entry. However, when performing the actual writes, msg_print_text() only writes the entry to the buffer if the written len is lesser than the size of the buffer. So if the lengths of the selected youngest log messages happen to precisely fill up the provided buffer, the last log message is not included. We don't want to modify msg_print_text() to fill up the buffer and start returning a length which is equal to the size of the buffer, since callers of its other users, such as kmsg_dump_get_line(), depend upon the current behaviour. Instead, fix kmsg_dump_get_buffer() to compensate for this. For example, with the following two final prints: [ 6.427502] AAAAAAAAAAAAA [ 6.427769] BBBBBBBB12345 A dump of a 64-byte buffer filled by kmsg_dump_get_buffer(), before this patch: 00000000: 3c 30 3e 5b 20 20 20 20 36 2e 35 32 32 31 39 37 <0>[ 6.522197 00000010: 5d 20 41 41 41 41 41 41 41 41 41 41 41 41 41 0a ] AAAAAAAAAAAAA. 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ After this patch: 00000000: 3c 30 3e 5b 20 20 20 20 36 2e 34 35 36 36 37 38 <0>[ 6.456678 00000010: 5d 20 42 42 42 42 42 42 42 42 31 32 33 34 35 0a ] BBBBBBBB12345. 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Link: http://lkml.kernel.org/r/20190711142937.4083-1-vincent.whitchurch@axis.com Fixes: e2ae715d66bf4bec ("kmsg - kmsg_dump() use iterator to receive log buffer content") To: rostedt@goodmis.org Cc: linux-kernel@vger.kernel.org Cc: # v3.5+ Signed-off-by: Vincent Whitchurch Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Greg Kroah-Hartman

printk: Wake klogd when passing console_lock owner

2018-12-17T08:28:55Z

[ Upstream commit c14376de3a1befa70d9811ca2872d47367b48767 ] wake_klogd is a local variable in console_unlock(). The information is lost when the console_lock owner using the busy wait added by the commit dbdda842fe96f8932 ("printk: Add console owner and waiter logic to load balance console writes"). The following race is possible: CPU0 CPU1 console_unlock() for (;;) /* calling console for last message */ printk() log_store() log_next_seq++; /* see new message */ if (seen_seq != log_next_seq) { wake_klogd = true; seen_seq = log_next_seq; } console_lock_spinning_enable(); if (console_trylock_spinning()) /* spinning */ if (console_lock_spinning_disable_and_check()) { printk_safe_exit_irqrestore(flags); return; console_unlock() if (seen_seq != log_next_seq) { /* already seen */ /* nothing to do */ Result: Nobody would wakeup klogd. One solution would be to make a global variable from wake_klogd. But then we would need to manipulate it under a lock or so. This patch wakes klogd also when console_lock is passed to the spinning waiter. It looks like the right way to go. Also userspace should have a chance to see and store any "flood" of messages. Note that the very late klogd wake up was a historic solution. It made sense on single CPU systems or when sys_syslog() operations were synchronized using the big kernel lock like in v2.1.113. But it is questionable these days. Fixes: dbdda842fe96f8932 ("printk: Add console owner and waiter logic to load balance console writes") Link: http://lkml.kernel.org/r/20180226155734.dzwg3aovqnwtvkoy@pathway.suse.cz Cc: Steven Rostedt Cc: linux-kernel@vger.kernel.org Cc: Tejun Heo Suggested-by: Sergey Senozhatsky Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

printk: Never set console_may_schedule in console_trylock()

2018-12-17T08:28:55Z

[ Upstream commit fd5f7cde1b85d4c8e09ca46ce948e008a2377f64 ] This patch, basically, reverts commit 6b97a20d3a79 ("printk: set may_schedule for some of console_trylock() callers"). That commit was a mistake, it introduced a big dependency on the scheduler, by enabling preemption under console_sem in printk()->console_unlock() path, which is rather too critical. The patch did not significantly reduce the possibilities of printk() lockups, but made it possible to stall printk(), as has been reported by Tetsuo Handa [1]. Another issues is that preemption under console_sem also messes up with Steven Rostedt's hand off scheme, by making it possible to sleep with console_sem both in console_unlock() and in vprintk_emit(), after acquiring the console_sem ownership (anywhere between printk_safe_exit_irqrestore() in console_trylock_spinning() and printk_safe_enter_irqsave() in console_unlock()). This makes hand off less likely and, at the same time, may result in a significant amount of pending logbuf messages. Preempted console_sem owner makes it impossible for other CPUs to emit logbuf messages, but does not make it impossible for other CPUs to append new messages to the logbuf. Reinstate the old behavior and make printk() non-preemptible. Should any printk() lockup reports arrive they must be handled in a different way. [1] http://lkml.kernel.org/r/201603022101.CAH73907.OVOOMFHFFtQJSL%20()%20I-love%20!%20SAKURA%20!%20ne%20!%20jp Fixes: 6b97a20d3a79 ("printk: set may_schedule for some of console_trylock() callers") Link: http://lkml.kernel.org/r/20180116044716.GE6607@jagdpanzerIV To: Tetsuo Handa Cc: Sergey Senozhatsky Cc: Tejun Heo Cc: akpm@linux-foundation.org Cc: linux-mm@kvack.org Cc: Cong Wang Cc: Dave Hansen Cc: Johannes Weiner Cc: Mel Gorman Cc: Michal Hocko Cc: Vlastimil Babka Cc: Peter Zijlstra Cc: Linus Torvalds Cc: Jan Kara Cc: Mathieu Desnoyers Cc: Byungchul Park Cc: Pavel Machek Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky Reported-by: Tetsuo Handa Reviewed-by: Steven Rostedt (VMware) Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

printk: Hide console waiter logic into helpers

2018-12-17T08:28:54Z

[ Upstream commit c162d5b4338d72deed61aa65ed0f2f4ba2bbc8ab ] The commit ("printk: Add console owner and waiter logic to load balance console writes") made vprintk_emit() and console_unlock() even more complicated. This patch extracts the new code into 3 helper functions. They should help to keep it rather self-contained. It will be easier to use and maintain. This patch just shuffles the existing code. It does not change the functionality. Link: http://lkml.kernel.org/r/20180112160837.GD24497@linux.suse Cc: akpm@linux-foundation.org Cc: linux-mm@kvack.org Cc: Cong Wang Cc: Dave Hansen Cc: Johannes Weiner Cc: Mel Gorman Cc: Michal Hocko Cc: Vlastimil Babka Cc: Peter Zijlstra Cc: Linus Torvalds Cc: Jan Kara Cc: Mathieu Desnoyers Cc: Tetsuo Handa Cc: rostedt@home.goodmis.org Cc: Byungchul Park Cc: Tejun Heo Cc: Pavel Machek Cc: linux-kernel@vger.kernel.org Reviewed-by: Steven Rostedt (VMware) Acked-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

printk: Add console owner and waiter logic to load balance console writes

2018-12-17T08:28:54Z

[ Upstream commit dbdda842fe96f8932bae554f0adf463c27c42bc7 ] This patch implements what I discussed in Kernel Summit. I added lockdep annotation (hopefully correctly), and it hasn't had any splats (since I fixed some bugs in the first iterations). It did catch problems when I had the owner covering too much. But now that the owner is only set when actively calling the consoles, lockdep has stayed quiet. Here's the design again: I added a "console_owner" which is set to a task that is actively writing to the consoles. It is *not* the same as the owner of the console_lock. It is only set when doing the calls to the console functions. It is protected by a console_owner_lock which is a raw spin lock. There is a console_waiter. This is set when there is an active console owner that is not current, and waiter is not set. This too is protected by console_owner_lock. In printk() when it tries to write to the consoles, we have: if (console_trylock()) console_unlock(); Now I added an else, which will check if there is an active owner, and no current waiter. If that is the case, then console_waiter is set, and the task goes into a spin until it is no longer set. When the active console owner finishes writing the current message to the consoles, it grabs the console_owner_lock and sees if there is a waiter, and clears console_owner. If there is a waiter, then it breaks out of the loop, clears the waiter flag (because that will release the waiter from its spin), and exits. Note, it does *not* release the console semaphore. Because it is a semaphore, there is no owner. Another task may release it. This means that the waiter is guaranteed to be the new console owner! Which it becomes. Then the waiter calls console_unlock() and continues to write to the consoles. If another task comes along and does a printk() it too can become the new waiter, and we wash rinse and repeat! By Petr Mladek about possible new deadlocks: The thing is that we move console_sem only to printk() call that normally calls console_unlock() as well. It means that the transferred owner should not bring new type of dependencies. As Steven said somewhere: "If there is a deadlock, it was there even before." We could look at it from this side. The possible deadlock would look like: CPU0 CPU1 console_unlock() console_owner = current; spin_lockA() printk() spin = true; while (...) call_console_drivers() spin_lockA() This would be a deadlock. CPU0 would wait for the lock A. While CPU1 would own the lockA and would wait for CPU0 to finish calling the console drivers and pass the console_sem owner. But if the above is true than the following scenario was already possible before: CPU0 spin_lockA() printk() console_unlock() call_console_drivers() spin_lockA() By other words, this deadlock was there even before. Such deadlocks are prevented by using printk_deferred() in the sections guarded by the lock A. By Steven Rostedt: To demonstrate the issue, this module has been shown to lock up a system with 4 CPUs and a slow console (like a serial console). It is also able to lock up a 8 CPU system with only a fast (VGA) console, by passing in "loops=100". The changes in this commit prevent this module from locking up the system. #include #include #include #include #include #include static bool stop_testing; static unsigned int loops = 1; static void preempt_printk_workfn(struct work_struct *work) { int i; while (!READ_ONCE(stop_testing)) { for (i = 0; i < loops && !READ_ONCE(stop_testing); i++) { preempt_disable(); pr_emerg("%5d%-75s\n", smp_processor_id(), " XXX NOPREEMPT"); preempt_enable(); } msleep(1); } } static struct work_struct __percpu *works; static void finish(void) { int cpu; WRITE_ONCE(stop_testing, true); for_each_online_cpu(cpu) flush_work(per_cpu_ptr(works, cpu)); free_percpu(works); } static int __init test_init(void) { int cpu; works = alloc_percpu(struct work_struct); if (!works) return -ENOMEM; /* * This is just a test module. This will break if you * do any CPU hot plugging between loading and * unloading the module. */ for_each_online_cpu(cpu) { struct work_struct *work = per_cpu_ptr(works, cpu); INIT_WORK(work, &preempt_printk_workfn); schedule_work_on(cpu, work); } return 0; } static void __exit test_exit(void) { finish(); } module_param(loops, uint, 0); module_init(test_init); module_exit(test_exit); MODULE_LICENSE("GPL"); Link: http://lkml.kernel.org/r/20180110132418.7080-2-pmladek@suse.com Cc: akpm@linux-foundation.org Cc: linux-mm@kvack.org Cc: Cong Wang Cc: Dave Hansen Cc: Johannes Weiner Cc: Mel Gorman Cc: Michal Hocko Cc: Vlastimil Babka Cc: Peter Zijlstra Cc: Linus Torvalds Cc: Jan Kara Cc: Mathieu Desnoyers Cc: Tetsuo Handa Cc: Byungchul Park Cc: Tejun Heo Cc: Pavel Machek Cc: linux-kernel@vger.kernel.org Signed-off-by: Steven Rostedt (VMware) [pmladek@suse.com: Commit message about possible deadlocks] Acked-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

Revert "printk: Never set console_may_schedule in console_trylock()"

2018-12-17T08:28:54Z

This reverts commit c9b8d580b3fb0ab65d37c372aef19a318fda3199. This is just a technical revert to make the printk fix apply cleanly, this patch will be re-picked in about 3 commits.

printk: Never set console_may_schedule in console_trylock()

2018-11-21T08:24:17Z

commit fd5f7cde1b85d4c8e09ca46ce948e008a2377f64 upstream. This patch, basically, reverts commit 6b97a20d3a79 ("printk: set may_schedule for some of console_trylock() callers"). That commit was a mistake, it introduced a big dependency on the scheduler, by enabling preemption under console_sem in printk()->console_unlock() path, which is rather too critical. The patch did not significantly reduce the possibilities of printk() lockups, but made it possible to stall printk(), as has been reported by Tetsuo Handa [1]. Another issues is that preemption under console_sem also messes up with Steven Rostedt's hand off scheme, by making it possible to sleep with console_sem both in console_unlock() and in vprintk_emit(), after acquiring the console_sem ownership (anywhere between printk_safe_exit_irqrestore() in console_trylock_spinning() and printk_safe_enter_irqsave() in console_unlock()). This makes hand off less likely and, at the same time, may result in a significant amount of pending logbuf messages. Preempted console_sem owner makes it impossible for other CPUs to emit logbuf messages, but does not make it impossible for other CPUs to append new messages to the logbuf. Reinstate the old behavior and make printk() non-preemptible. Should any printk() lockup reports arrive they must be handled in a different way. [1] http://lkml.kernel.org/r/201603022101.CAH73907.OVOOMFHFFtQJSL%20()%20I-love%20!%20SAKURA%20!%20ne%20!%20jp Fixes: 6b97a20d3a79 ("printk: set may_schedule for some of console_trylock() callers") Link: http://lkml.kernel.org/r/20180116044716.GE6607@jagdpanzerIV To: Tetsuo Handa Cc: Sergey Senozhatsky Cc: Tejun Heo Cc: akpm@linux-foundation.org Cc: linux-mm@kvack.org Cc: Cong Wang Cc: Dave Hansen Cc: Johannes Weiner Cc: Mel Gorman Cc: Michal Hocko Cc: Vlastimil Babka Cc: Peter Zijlstra Cc: Linus Torvalds Cc: Jan Kara Cc: Mathieu Desnoyers Cc: Byungchul Park Cc: Pavel Machek Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky Reported-by: Tetsuo Handa Reviewed-by: Steven Rostedt (VMware) Signed-off-by: Petr Mladek Signed-off-by: Sudip Mukherjee Signed-off-by: Greg Kroah-Hartman

printk: Fix panic caused by passing log_buf_len to command line

2018-11-13T19:15:09Z

commit 277fcdb2cfee38ccdbe07e705dbd4896ba0c9930 upstream. log_buf_len_setup does not check input argument before passing it to simple_strtoull. The argument would be a NULL pointer if "log_buf_len", without its value, is set in command line and thus causes the following panic. PANIC: early exception 0xe3 IP 10:ffffffffaaeacd0d error 0 cr2 0x0 [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc4-yocto-standard+ #1 [ 0.000000] RIP: 0010:_parse_integer_fixup_radix+0xd/0x70 ... [ 0.000000] Call Trace: [ 0.000000] simple_strtoull+0x29/0x70 [ 0.000000] memparse+0x26/0x90 [ 0.000000] log_buf_len_setup+0x17/0x22 [ 0.000000] do_early_param+0x57/0x8e [ 0.000000] parse_args+0x208/0x320 [ 0.000000] ? rdinit_setup+0x30/0x30 [ 0.000000] parse_early_options+0x29/0x2d [ 0.000000] ? rdinit_setup+0x30/0x30 [ 0.000000] parse_early_param+0x36/0x4d [ 0.000000] setup_arch+0x336/0x99e [ 0.000000] start_kernel+0x6f/0x4ee [ 0.000000] x86_64_start_reservations+0x24/0x26 [ 0.000000] x86_64_start_kernel+0x6f/0x72 [ 0.000000] secondary_startup_64+0xa4/0xb0 This patch adds a check to prevent the panic. Link: http://lkml.kernel.org/r/1538239553-81805-1-git-send-email-zhe.he@windriver.com Cc: stable@vger.kernel.org Cc: rostedt@goodmis.org Cc: linux-kernel@vger.kernel.org Signed-off-by: He Zhe Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Greg Kroah-Hartman

printk/tracing: Do not trace printk_nmi_enter()

2018-09-09T17:55:57Z

commit d1c392c9e2a301f38998a353f467f76414e38725 upstream. I hit the following splat in my tests: ------------[ cut here ]------------ IRQs not enabled as expected WARNING: CPU: 3 PID: 0 at kernel/time/tick-sched.c:982 tick_nohz_idle_enter+0x44/0x8c Modules linked in: ip6t_REJECT nf_reject_ipv6 ip6table_filter ip6_tables ipv6 CPU: 3 PID: 0 Comm: swapper/3 Not tainted 4.19.0-rc2-test+ #2 Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1.6 02/22/2014 EIP: tick_nohz_idle_enter+0x44/0x8c Code: ec 05 00 00 00 75 26 83 b8 c0 05 00 00 00 75 1d 80 3d d0 36 3e c1 00 75 14 68 94 63 12 c1 c6 05 d0 36 3e c1 01 e8 04 ee f8 ff <0f> 0b 58 fa bb a0 e5 66 c1 e8 25 0f 04 00 64 03 1d 28 31 52 c1 8b EAX: 0000001c EBX: f26e7f8c ECX: 00000006 EDX: 00000007 ESI: f26dd1c0 EDI: 00000000 EBP: f26e7f40 ESP: f26e7f38 DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00010296 CR0: 80050033 CR2: 0813c6b0 CR3: 2f342000 CR4: 001406f0 Call Trace: do_idle+0x33/0x202 cpu_startup_entry+0x61/0x63 start_secondary+0x18e/0x1ed startup_32_smp+0x164/0x168 irq event stamp: 18773830 hardirqs last enabled at (18773829): [] trace_hardirqs_on_thunk+0xc/0x10 hardirqs last disabled at (18773830): [] trace_hardirqs_off_thunk+0xc/0x10 softirqs last enabled at (18773824): [] __do_softirq+0x25f/0x2bf softirqs last disabled at (18773767): [] call_on_stack+0x45/0x4b ---[ end trace b7c64aa79e17954a ]--- After a bit of debugging, I found what was happening. This would trigger when performing "perf" with a high NMI interrupt rate, while enabling and disabling function tracer. Ftrace uses breakpoints to convert the nops at the start of functions to calls to the function trampolines. The breakpoint traps disable interrupts and this makes calls into lockdep via the trace_hardirqs_off_thunk in the entry.S code. What happens is the following: do_idle { [interrupts enabled] [interrupts disabled] TRACE_IRQS_OFF [lockdep says irqs off] [...] TRACE_IRQS_IRET test if pt_regs say return to interrupts enabled [yes] TRACE_IRQS_ON [lockdep says irqs are on] nmi_enter() { printk_nmi_enter() [traced by ftrace] [ hit ftrace breakpoint ] TRACE_IRQS_OFF [lockdep says irqs off] [...] TRACE_IRQS_IRET [return from breakpoint] test if pt_regs say interrupts enabled [no] [iret back to interrupt] [iret back to code] tick_nohz_idle_enter() { lockdep_assert_irqs_enabled() [lockdep say no!] Although interrupts are indeed enabled, lockdep thinks it is not, and since we now do asserts via lockdep, it gives a false warning. The issue here is that printk_nmi_enter() is called before lockdep_off(), which disables lockdep (for this reason) in NMIs. By simply not allowing ftrace to see printk_nmi_enter() (via notrace annotation) we keep lockdep from getting confused. Cc: stable@vger.kernel.org Fixes: 42a0bb3f71383 ("printk/nmi: generic solution for safe printk in NMI") Acked-by: Sergey Senozhatsky Acked-by: Petr Mladek Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Greg Kroah-Hartman