| Message ID | 20231213000452.88295-9-graf@amazon.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | kexec: Allow preservation of ftrace buffers | expand |
On Wed, 13 Dec 2023 00:04:45 +0000 Alexander Graf <graf@amazon.com> wrote: > With KHO (Kexec HandOver), we want to preserve trace buffers across > kexec. To carry over their state between kernels, the kernel needs a > common handle for them that exists on both sides. As handle we introduce > names for ring buffers. In a follow-up patch, the kernel can then use > these names to recover buffer contents for specific ring buffers. > Is there a way to use the trace_array name instead? The trace_array is the structure that represents each tracing instance. And it already has a name field. And if you can get the associated ring buffer from that too. struct trace_array *tr; tr->array_buffer.buffer tr->name When you do: mkdir /sys/kernel/tracing/instance/foo You create a new trace_array instance where tr->name = "foo" and allocates the buffer for it as well. -- Steve
Hi Steve, On 13.12.23 01:15, Steven Rostedt wrote: > > On Wed, 13 Dec 2023 00:04:45 +0000 > Alexander Graf <graf@amazon.com> wrote: > >> With KHO (Kexec HandOver), we want to preserve trace buffers across >> kexec. To carry over their state between kernels, the kernel needs a >> common handle for them that exists on both sides. As handle we introduce >> names for ring buffers. In a follow-up patch, the kernel can then use >> these names to recover buffer contents for specific ring buffers. >> > Is there a way to use the trace_array name instead? > > The trace_array is the structure that represents each tracing instance. And > it already has a name field. And if you can get the associated ring buffer > from that too. > > struct trace_array *tr; > > tr->array_buffer.buffer > > tr->name > > When you do: mkdir /sys/kernel/tracing/instance/foo > > You create a new trace_array instance where tr->name = "foo" and allocates > the buffer for it as well. The name in the ring buffer is pretty much just a copy of the trace array name. I use it to reconstruct which buffer we're actually referring to inside __ring_buffer_alloc(). I'm all ears for alternative suggestions. I suppose we could pass tr as argument to ring_buffer_alloc() instead of the name? Alex Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
On Wed, 13 Dec 2023 01:35:16 +0100 Alexander Graf <graf@amazon.com> wrote: > > The trace_array is the structure that represents each tracing instance. And > > it already has a name field. And if you can get the associated ring buffer > > from that too. > > > > struct trace_array *tr; > > > > tr->array_buffer.buffer > > > > tr->name > > > > When you do: mkdir /sys/kernel/tracing/instance/foo > > > > You create a new trace_array instance where tr->name = "foo" and allocates > > the buffer for it as well. > > The name in the ring buffer is pretty much just a copy of the trace > array name. I use it to reconstruct which buffer we're actually > referring to inside __ring_buffer_alloc(). No, I rather not tie the ring buffer to the trace_array. > > I'm all ears for alternative suggestions. I suppose we could pass tr as > argument to ring_buffer_alloc() instead of the name? I'll have to spend some time (that I don't currently have :-( ) on looking at this more. I really don't like the copying of the name into the ring buffer allocation, as it may be an unneeded burden to maintain, not to mention the duplicate field. -- Steve
Hi Alexander, kernel test robot noticed the following build errors: [auto build test ERROR on tip/x86/core] [also build test ERROR on arm64/for-next/core akpm-mm/mm-everything linus/master v6.7-rc5 next-20231213] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch#_base_tree_information] url: https://github.com/intel-lab-lkp/linux/commits/Alexander-Graf/mm-memblock-Add-support-for-scratch-memory/20231213-080941 base: tip/x86/core patch link: https://lore.kernel.org/r/20231213000452.88295-9-graf%40amazon.com patch subject: [PATCH 08/15] tracing: Introduce names for ring buffers config: i386-buildonly-randconfig-003-20231213 (https://download.01.org/0day-ci/archive/20231213/202312131922.5dJORQu4-lkp@intel.com/config) compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07) reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231213/202312131922.5dJORQu4-lkp@intel.com/reproduce) If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags | Reported-by: kernel test robot <lkp@intel.com> | Closes: https://lore.kernel.org/oe-kbuild-all/202312131922.5dJORQu4-lkp@intel.com/ All errors (new ones prefixed by >>): >> kernel/trace/ring_buffer_benchmark.c:435:53: error: too few arguments provided to function-like macro invocation buffer = ring_buffer_alloc(1000000, RB_FL_OVERWRITE); ^ include/linux/ring_buffer.h:96:9: note: macro 'ring_buffer_alloc' defined here #define ring_buffer_alloc(name, size, flags) \ ^ >> kernel/trace/ring_buffer_benchmark.c:435:11: error: use of undeclared identifier 'ring_buffer_alloc'; did you mean '__ring_buffer_alloc'? buffer = ring_buffer_alloc(1000000, RB_FL_OVERWRITE); ^~~~~~~~~~~~~~~~~ __ring_buffer_alloc include/linux/ring_buffer.h:88:1: note: '__ring_buffer_alloc' declared here __ring_buffer_alloc(const char *name, unsigned long size, unsigned flags, ^ 2 errors generated. -- >> kernel/trace/ring_buffer.c:6096:65: error: too few arguments provided to function-like macro invocation buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE); ^ include/linux/ring_buffer.h:96:9: note: macro 'ring_buffer_alloc' defined here #define ring_buffer_alloc(name, size, flags) \ ^ >> kernel/trace/ring_buffer.c:6096:11: error: use of undeclared identifier 'ring_buffer_alloc'; did you mean '__ring_buffer_alloc'? buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE); ^~~~~~~~~~~~~~~~~ __ring_buffer_alloc kernel/trace/ring_buffer.c:1873:19: note: '__ring_buffer_alloc' declared here EXPORT_SYMBOL_GPL(__ring_buffer_alloc); ^ 2 errors generated. vim +435 kernel/trace/ring_buffer_benchmark.c 5092dbc96f3acd Steven Rostedt 2009-05-05 429 5092dbc96f3acd Steven Rostedt 2009-05-05 430 static int __init ring_buffer_benchmark_init(void) 5092dbc96f3acd Steven Rostedt 2009-05-05 431 { 5092dbc96f3acd Steven Rostedt 2009-05-05 432 int ret; 5092dbc96f3acd Steven Rostedt 2009-05-05 433 5092dbc96f3acd Steven Rostedt 2009-05-05 434 /* make a one meg buffer in overwite mode */ 5092dbc96f3acd Steven Rostedt 2009-05-05 @435 buffer = ring_buffer_alloc(1000000, RB_FL_OVERWRITE); 5092dbc96f3acd Steven Rostedt 2009-05-05 436 if (!buffer) 5092dbc96f3acd Steven Rostedt 2009-05-05 437 return -ENOMEM; 5092dbc96f3acd Steven Rostedt 2009-05-05 438 5092dbc96f3acd Steven Rostedt 2009-05-05 439 if (!disable_reader) { 5092dbc96f3acd Steven Rostedt 2009-05-05 440 consumer = kthread_create(ring_buffer_consumer_thread, 5092dbc96f3acd Steven Rostedt 2009-05-05 441 NULL, "rb_consumer"); 5092dbc96f3acd Steven Rostedt 2009-05-05 442 ret = PTR_ERR(consumer); 5092dbc96f3acd Steven Rostedt 2009-05-05 443 if (IS_ERR(consumer)) 5092dbc96f3acd Steven Rostedt 2009-05-05 444 goto out_fail; 5092dbc96f3acd Steven Rostedt 2009-05-05 445 } 5092dbc96f3acd Steven Rostedt 2009-05-05 446 5092dbc96f3acd Steven Rostedt 2009-05-05 447 producer = kthread_run(ring_buffer_producer_thread, 5092dbc96f3acd Steven Rostedt 2009-05-05 448 NULL, "rb_producer"); 5092dbc96f3acd Steven Rostedt 2009-05-05 449 ret = PTR_ERR(producer); 5092dbc96f3acd Steven Rostedt 2009-05-05 450 5092dbc96f3acd Steven Rostedt 2009-05-05 451 if (IS_ERR(producer)) 5092dbc96f3acd Steven Rostedt 2009-05-05 452 goto out_kill; 5092dbc96f3acd Steven Rostedt 2009-05-05 453 98e4833ba3c314 Ingo Molnar 2009-11-23 454 /* 98e4833ba3c314 Ingo Molnar 2009-11-23 455 * Run them as low-prio background tasks by default: 98e4833ba3c314 Ingo Molnar 2009-11-23 456 */ 7ac07434048001 Steven Rostedt 2009-11-25 457 if (!disable_reader) { 4fd5750af02ab7 Peter Zijlstra 2020-07-20 458 if (consumer_fifo >= 2) 4fd5750af02ab7 Peter Zijlstra 2020-07-20 459 sched_set_fifo(consumer); 4fd5750af02ab7 Peter Zijlstra 2020-07-20 460 else if (consumer_fifo == 1) 4fd5750af02ab7 Peter Zijlstra 2020-07-20 461 sched_set_fifo_low(consumer); 4fd5750af02ab7 Peter Zijlstra 2020-07-20 462 else 7ac07434048001 Steven Rostedt 2009-11-25 463 set_user_nice(consumer, consumer_nice); 7ac07434048001 Steven Rostedt 2009-11-25 464 } 7ac07434048001 Steven Rostedt 2009-11-25 465 4fd5750af02ab7 Peter Zijlstra 2020-07-20 466 if (producer_fifo >= 2) 4fd5750af02ab7 Peter Zijlstra 2020-07-20 467 sched_set_fifo(producer); 4fd5750af02ab7 Peter Zijlstra 2020-07-20 468 else if (producer_fifo == 1) 4fd5750af02ab7 Peter Zijlstra 2020-07-20 469 sched_set_fifo_low(producer); 4fd5750af02ab7 Peter Zijlstra 2020-07-20 470 else 7ac07434048001 Steven Rostedt 2009-11-25 471 set_user_nice(producer, producer_nice); 98e4833ba3c314 Ingo Molnar 2009-11-23 472 5092dbc96f3acd Steven Rostedt 2009-05-05 473 return 0; 5092dbc96f3acd Steven Rostedt 2009-05-05 474 5092dbc96f3acd Steven Rostedt 2009-05-05 475 out_kill: 5092dbc96f3acd Steven Rostedt 2009-05-05 476 if (consumer) 5092dbc96f3acd Steven Rostedt 2009-05-05 477 kthread_stop(consumer); 5092dbc96f3acd Steven Rostedt 2009-05-05 478 5092dbc96f3acd Steven Rostedt 2009-05-05 479 out_fail: 5092dbc96f3acd Steven Rostedt 2009-05-05 480 ring_buffer_free(buffer); 5092dbc96f3acd Steven Rostedt 2009-05-05 481 return ret; 5092dbc96f3acd Steven Rostedt 2009-05-05 482 } 5092dbc96f3acd Steven Rostedt 2009-05-05 483
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 782e14f62201..f34538f97c75 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -85,17 +85,18 @@ void ring_buffer_discard_commit(struct trace_buffer *buffer, * size is in bytes for each per CPU buffer. */ struct trace_buffer * -__ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *key); +__ring_buffer_alloc(const char *name, unsigned long size, unsigned flags, + struct lock_class_key *key); /* * Because the ring buffer is generic, if other users of the ring buffer get * traced by ftrace, it can produce lockdep warnings. We need to keep each * ring buffer's lock class separate. */ -#define ring_buffer_alloc(size, flags) \ +#define ring_buffer_alloc(name, size, flags) \ ({ \ static struct lock_class_key __key; \ - __ring_buffer_alloc((size), (flags), &__key); \ + __ring_buffer_alloc((name), (size), (flags), &__key); \ }) int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full); diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 43cc47d7faaf..eaaf823ddedb 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -557,6 +557,7 @@ struct trace_buffer { struct rb_irq_work irq_work; bool time_stamp_abs; + const char *name; }; struct ring_buffer_iter { @@ -1801,7 +1802,8 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer) * when the buffer wraps. If this flag is not set, the buffer will * drop data when the tail hits the head. */ -struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags, +struct trace_buffer *__ring_buffer_alloc(const char *name, + unsigned long size, unsigned flags, struct lock_class_key *key) { struct trace_buffer *buffer; @@ -1823,6 +1825,7 @@ struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags, buffer->flags = flags; buffer->clock = trace_clock_local; buffer->reader_lock_key = key; + buffer->name = name; init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters); init_waitqueue_head(&buffer->irq_work.waiters); diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 9aebf904ff97..7700ca1be2a5 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -9384,7 +9384,8 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size buf->tr = tr; - buf->buffer = ring_buffer_alloc(size, rb_flags); + buf->buffer = ring_buffer_alloc(tr->name ? tr->name : "global_trace", + size, rb_flags); if (!buf->buffer) return -ENOMEM; @@ -9421,7 +9422,7 @@ static int allocate_trace_buffers(struct trace_array *tr, int size) return ret; #ifdef CONFIG_TRACER_MAX_TRACE - ret = allocate_trace_buffer(tr, &tr->max_buffer, + ret = allocate_trace_buffer(NULL, &tr->max_buffer, allocate_snapshot ? size : 1); if (MEM_FAIL(ret, "Failed to allocate trace buffer\n")) { free_trace_buffer(&tr->array_buffer); @@ -10473,7 +10474,7 @@ __init static int tracer_alloc_buffers(void) goto out_free_cpumask; /* Used for event triggers */ ret = -ENOMEM; - temp_buffer = ring_buffer_alloc(PAGE_SIZE, RB_FL_OVERWRITE); + temp_buffer = ring_buffer_alloc("temp_buffer", PAGE_SIZE, RB_FL_OVERWRITE); if (!temp_buffer) goto out_rm_hp_state;
With KHO (Kexec HandOver), we want to preserve trace buffers across kexec. To carry over their state between kernels, the kernel needs a common handle for them that exists on both sides. As handle we introduce names for ring buffers. In a follow-up patch, the kernel can then use these names to recover buffer contents for specific ring buffers. Signed-off-by: Alexander Graf <graf@amazon.com> --- include/linux/ring_buffer.h | 7 ++++--- kernel/trace/ring_buffer.c | 5 ++++- kernel/trace/trace.c | 7 ++++--- 3 files changed, 12 insertions(+), 7 deletions(-)