@@ -507,6 +507,7 @@ struct ring_buffer_per_cpu {
unsigned long pages_removed;
unsigned int mapped;
+ unsigned int user_mapped; /* first user space mapping */
struct mutex mapping_lock;
unsigned long *subbuf_ids; /* ID to subbuf VA */
struct trace_buffer_meta *meta_page;
@@ -1710,6 +1711,7 @@ static int rb_read_data_buffer(struct buffer_data_page *dpage, int tail, int cpu
case RINGBUF_TYPE_TIME_STAMP:
delta = rb_event_time_stamp(event);
+ delta = rb_fix_abs_ts(delta, ts);
if (delta < ts) {
*delta_ptr = delta;
*timestamp = ts;
@@ -6879,7 +6881,7 @@ static int __rb_inc_dec_mapped(struct ring_buffer_per_cpu *cpu_buffer,
if (inc && cpu_buffer->mapped == UINT_MAX)
return -EBUSY;
- if (WARN_ON(!inc && cpu_buffer->mapped == 0))
+ if (WARN_ON(!inc && cpu_buffer->mapped < cpu_buffer->user_mapped))
return -EINVAL;
mutex_lock(&cpu_buffer->buffer->mutex);
@@ -7013,7 +7015,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
mutex_lock(&cpu_buffer->mapping_lock);
- if (cpu_buffer->mapped) {
+ if (cpu_buffer->user_mapped) {
err = __rb_map_vma(cpu_buffer, vma);
if (!err)
err = __rb_inc_dec_mapped(cpu_buffer, true);
@@ -7050,7 +7052,9 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
err = __rb_map_vma(cpu_buffer, vma);
if (!err) {
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+ /* This is the first time it is mapped externally */
cpu_buffer->mapped++;
+ cpu_buffer->user_mapped = cpu_buffer->mapped;
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
} else {
kfree(cpu_buffer->subbuf_ids);
@@ -7078,10 +7082,10 @@ int ring_buffer_unmap(struct trace_buffer *buffer, int cpu)
mutex_lock(&cpu_buffer->mapping_lock);
- if (!cpu_buffer->mapped) {
+ if (!cpu_buffer->user_mapped) {
err = -ENODEV;
goto out;
- } else if (cpu_buffer->mapped > 1) {
+ } else if (cpu_buffer->mapped > cpu_buffer->user_mapped) {
__rb_inc_dec_mapped(cpu_buffer, false);
goto out;
}
@@ -7089,8 +7093,10 @@ int ring_buffer_unmap(struct trace_buffer *buffer, int cpu)
mutex_lock(&buffer->mutex);
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
- WARN_ON_ONCE(!cpu_buffer->mapped);
- cpu_buffer->mapped--;
+ /* This is the last user space mapping */
+ if (!WARN_ON_ONCE(cpu_buffer->mapped != cpu_buffer->user_mapped))
+ cpu_buffer->mapped--;
+ cpu_buffer->user_mapped = 0;
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
This is a way to map a ring buffer instance across reboots. The requirement is that you have a memory region that is not erased. I tested this on a Debian VM running on qemu on a Debian server, and even tested it on a baremetal box running Fedora. I was surprised that it worked on the baremetal box, but it does so surprisingly consistently. This series does not require the ring buffer mapping, but simply takes a physical address that has been reserved via memmap (on x86 only) An example of the kernel command line is: memmap=12M$0x285400000 trace_instance=boot_mapped@0x285400000:12M The above will reserve 12M at physical address 0x285400000 (done by the existing memmap command line option), and then the trace_instance option was extended to take an address and size (@0x285400000:12M). It will then vmap() that address and allocate a ring buffer in it. If a ring buffer already exists, it will use it and expose the contents to user space. The memory reserved is used by the ring buffer of this instance. It acts like a memory mapped instance so it has some limitations. It does not allow snapshots nor does it allow tracers which use a snapshot buffer (like irqsoff and wakeup tracers). On boot up, when setting up the ring buffer, it looks at the current content and does a vigorous test to see if the content is valid. It even walks the events in all the sub-buffers to make sure the ring buffer meta data is correct. If it determines that the content is valid, it will reconstruct the ring buffer to use the content it has found. If the buffer is valid, on the next boot, the boot_mapped instance will contain the data from the previous boot. You can cat the trace or trace_pipe file, or even run trace-cmd extract on it to make a trace.dat file that holds the date. This is much better than dealing with a ftrace_dump_on_opps (I wish I had this a decade ago!) There are still some limitations of this buffer. One is that it assumes that the kernel you are booting back into is the same one that crashed. At least the trace_events (like sched_switch and friends) all have the same ids. This would be true with the same kernel as the ids are determined at link time. Module events could possible be a problem as the ids may not match. This version of the patch series saves a text function and a data string address in the persistent memory, and this is used to calculate the delta between text and data addresses of the new boot up. Now function tracing and "%pS" still work across boots. Even the RCU trace events that point to static strings work as well! The delta is exported by a new file in the instance called "last_boot_info" that has something like this: # cat last_boot_info text delta: -268435456 data delta: -268435456 This can be used by trace-cmd that reads the trace_pipe_raw data and now can figure out how to map the print_formats and kallsyms to the raw data in the buffers. This can be used to debug kernel shutdown. I ran the following: # trace-cmd start -B boot_mapped -p function # reboot [after reboot] # trace-cmd show -B boot_mapped | tail -20 swapper/0-1 [000] d..1. 63.479667: preempt_count_add <-delay_tsc swapper/0-1 [000] d..2. 63.479669: preempt_count_sub <-delay_tsc swapper/0-1 [000] d..1. 63.479671: disable_local_APIC <-native_stop_other_cpus swapper/0-1 [000] d..1. 63.479673: clear_local_APIC.part.0 <-disable_local_APIC swapper/0-1 [000] d..1. 63.479716: mcheck_cpu_clear <-native_stop_other_cpus swapper/0-1 [000] d..1. 63.479718: mce_intel_feature_clear <-native_stop_other_cpus swapper/0-1 [000] d..1. 63.479720: lmce_supported <-mce_intel_feature_clear swapper/0-1 [000] d..1. 63.479732: lapic_shutdown <-native_machine_shutdown swapper/0-1 [000] d..1. 63.479735: disable_local_APIC <-native_machine_shutdown swapper/0-1 [000] d..1. 63.479736: clear_local_APIC.part.0 <-disable_local_APIC swapper/0-1 [000] d..1. 63.479763: restore_boot_irq_mode <-native_machine_shutdown swapper/0-1 [000] d..1. 63.479763: native_restore_boot_irq_mode <-native_machine_shutdown swapper/0-1 [000] d..1. 63.479764: disconnect_bsp_APIC <-native_machine_shutdown swapper/0-1 [000] d..1. 63.479777: hpet_disable <-native_machine_shutdown swapper/0-1 [000] d..1. 63.479778: iommu_shutdown_noop <-native_machine_restart swapper/0-1 [000] d..1. 63.479779: native_machine_emergency_restart <-__do_sys_reboot swapper/0-1 [000] d..1. 63.479779: tboot_shutdown <-native_machine_emergency_restart swapper/0-1 [000] d..1. 63.479790: acpi_reboot <-native_machine_emergency_restart swapper/0-1 [000] d..1. 63.479791: acpi_reset <-acpi_reboot swapper/0-1 [000] d..1. 63.479791: acpi_os_write_port <-acpi_reboot Enjoy... Changes since v4: https://lore.kernel.org/all/20240611192828.691638177@goodmis.org/ [ Diff between v3 at bottom ] - Fixed "mapped" variable for per cpu ring buffers for when the first user space mapping happens. Added "user_mapped" that gets set the first time the ring buffer is mapped to user space, and this is used to compare the mapped counter. - Added back the delta = rb_fix_abs_ts(delta, ts) in the validate time stamp code. This was accidentally removed when copying the validate time stamp debug code to the validate persistent buffer code. Changes since v3: https://lore.kernel.org/all/20240606211735.684785459@goodmis.org/ - Removed an unused variable - Fixed enable_instances() as the path without memory using the memory location in the command line parameter passed in "tok" where it now needs to be "name" for creating the snapshot buffer, otherwise it would pass in NULL which could crash the kernel on boot. Changes since v2: https://lore.kernel.org/all/20240411012541.285904543@goodmis.org/ - Rebased on top of 6.10-rc2 that has the memory mapped ring buffer code. - Added hard coded address to map to (from memmap=nn$ss), instead of relying on using reserve_mem (which I still want to add). - Updated comments - Restructured the validate code as the previous version broke the ring buffer timestamp validation code. Steven Rostedt (Google) (13): ring-buffer: Allow mapped field to be set without mapping ring-buffer: Add ring_buffer_alloc_range() ring-buffer: Add ring_buffer_meta data tracing: Implement creating an instance based on a given memory region ring-buffer: Add output of ring buffer meta page ring-buffer: Add test if range of boot buffer is valid ring-buffer: Validate boot range memory events tracing: Add option to use memmapped memory for trace boot instance ring-buffer: Save text and data locations in mapped meta data tracing/ring-buffer: Add last_boot_info file to boot instance tracing: Handle old buffer mappings for event strings and functions tracing: Update function tracing output for previous boot buffer tracing: Add last boot delta offset for stack traces ---- Documentation/admin-guide/kernel-parameters.txt | 9 + include/linux/ring_buffer.h | 20 + kernel/trace/ring_buffer.c | 867 +++++++++++++++++++++--- kernel/trace/trace.c | 242 ++++++- kernel/trace/trace.h | 8 + kernel/trace/trace_output.c | 12 +- 6 files changed, 1046 insertions(+), 112 deletions(-)