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![Douglas Anderson](/assets/img/avatar_default.png)
As reported back in 2016-11 [1], the "ftdump" kdb command triggers a BUG for "sleeping function called from invalid context". kdb's "ftdump" command wants to call ring_buffer_read_prepare() in atomic context. A very simple solution for this is to add allocation flags to ring_buffer_read_prepare() so kdb can call it without triggering the allocation error. This patch does that. Note that in the original email thread about this, it was suggested that perhaps the solution for kdb was to either preallocate the buffer ahead of time or create our own iterator. I'm hoping that this alternative of adding allocation flags to ring_buffer_read_prepare() can be considered since it means I don't need to duplicate more of the core trace code into "trace_kdb.c" (for either creating my own iterator or re-preparing a ring allocator whose memory was already allocated). NOTE: another option for kdb is to actually figure out how to make it reuse the existing ftrace_dump() function and totally eliminate the duplication. This sounds very appealing and actually works (the "sr z" command can be seen to properly dump the ftrace buffer). The downside here is that ftrace_dump() fully consumes the trace buffer. Unless that is changed I'd rather not use it because it means "ftdump | grep xyz" won't be very useful to search the ftrace buffer since it will throw away the whole trace on the first grep. A future patch to dump only the last few lines of the buffer will also be hard to implement. [1] https://lkml.kernel.org/r/20161117191605.GA21459@google.com Link: http://lkml.kernel.org/r/20190308193205.213659-1-dianders@chromium.org Reported-by: Brian Norris <briannorris@chromium.org> Signed-off-by: Douglas Anderson <dianders@chromium.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
213 lines
7.3 KiB
C
213 lines
7.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_RING_BUFFER_H
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#define _LINUX_RING_BUFFER_H
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#include <linux/mm.h>
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#include <linux/seq_file.h>
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#include <linux/poll.h>
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struct ring_buffer;
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struct ring_buffer_iter;
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/*
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* Don't refer to this struct directly, use functions below.
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*/
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struct ring_buffer_event {
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u32 type_len:5, time_delta:27;
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u32 array[];
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};
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/**
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* enum ring_buffer_type - internal ring buffer types
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*
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* @RINGBUF_TYPE_PADDING: Left over page padding or discarded event
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* If time_delta is 0:
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* array is ignored
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* size is variable depending on how much
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* padding is needed
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* If time_delta is non zero:
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* array[0] holds the actual length
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* size = 4 + length (bytes)
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*
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* @RINGBUF_TYPE_TIME_EXTEND: Extend the time delta
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* array[0] = time delta (28 .. 59)
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* size = 8 bytes
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*
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* @RINGBUF_TYPE_TIME_STAMP: Absolute timestamp
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* Same format as TIME_EXTEND except that the
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* value is an absolute timestamp, not a delta
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* event.time_delta contains bottom 27 bits
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* array[0] = top (28 .. 59) bits
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* size = 8 bytes
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*
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* <= @RINGBUF_TYPE_DATA_TYPE_LEN_MAX:
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* Data record
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* If type_len is zero:
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* array[0] holds the actual length
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* array[1..(length+3)/4] holds data
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* size = 4 + length (bytes)
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* else
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* length = type_len << 2
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* array[0..(length+3)/4-1] holds data
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* size = 4 + length (bytes)
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*/
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enum ring_buffer_type {
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RINGBUF_TYPE_DATA_TYPE_LEN_MAX = 28,
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RINGBUF_TYPE_PADDING,
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RINGBUF_TYPE_TIME_EXTEND,
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RINGBUF_TYPE_TIME_STAMP,
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};
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unsigned ring_buffer_event_length(struct ring_buffer_event *event);
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void *ring_buffer_event_data(struct ring_buffer_event *event);
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u64 ring_buffer_event_time_stamp(struct ring_buffer_event *event);
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/*
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* ring_buffer_discard_commit will remove an event that has not
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* been committed yet. If this is used, then ring_buffer_unlock_commit
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* must not be called on the discarded event. This function
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* will try to remove the event from the ring buffer completely
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* if another event has not been written after it.
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*
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* Example use:
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*
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* if (some_condition)
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* ring_buffer_discard_commit(buffer, event);
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* else
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* ring_buffer_unlock_commit(buffer, event);
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*/
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void ring_buffer_discard_commit(struct ring_buffer *buffer,
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struct ring_buffer_event *event);
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/*
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* size is in bytes for each per CPU buffer.
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*/
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struct ring_buffer *
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__ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *key);
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/*
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* Because the ring buffer is generic, if other users of the ring buffer get
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* traced by ftrace, it can produce lockdep warnings. We need to keep each
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* ring buffer's lock class separate.
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*/
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#define ring_buffer_alloc(size, flags) \
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({ \
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static struct lock_class_key __key; \
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__ring_buffer_alloc((size), (flags), &__key); \
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})
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int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full);
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__poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
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struct file *filp, poll_table *poll_table);
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#define RING_BUFFER_ALL_CPUS -1
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void ring_buffer_free(struct ring_buffer *buffer);
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int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size, int cpu);
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void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val);
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struct ring_buffer_event *ring_buffer_lock_reserve(struct ring_buffer *buffer,
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unsigned long length);
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int ring_buffer_unlock_commit(struct ring_buffer *buffer,
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struct ring_buffer_event *event);
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int ring_buffer_write(struct ring_buffer *buffer,
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unsigned long length, void *data);
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void ring_buffer_nest_start(struct ring_buffer *buffer);
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void ring_buffer_nest_end(struct ring_buffer *buffer);
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struct ring_buffer_event *
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ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts,
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unsigned long *lost_events);
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struct ring_buffer_event *
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ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
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unsigned long *lost_events);
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struct ring_buffer_iter *
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ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu, gfp_t flags);
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void ring_buffer_read_prepare_sync(void);
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void ring_buffer_read_start(struct ring_buffer_iter *iter);
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void ring_buffer_read_finish(struct ring_buffer_iter *iter);
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struct ring_buffer_event *
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ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts);
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struct ring_buffer_event *
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ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts);
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void ring_buffer_iter_reset(struct ring_buffer_iter *iter);
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int ring_buffer_iter_empty(struct ring_buffer_iter *iter);
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unsigned long ring_buffer_size(struct ring_buffer *buffer, int cpu);
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void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu);
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void ring_buffer_reset(struct ring_buffer *buffer);
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#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
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int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
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struct ring_buffer *buffer_b, int cpu);
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#else
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static inline int
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ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
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struct ring_buffer *buffer_b, int cpu)
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{
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return -ENODEV;
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}
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#endif
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bool ring_buffer_empty(struct ring_buffer *buffer);
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bool ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu);
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void ring_buffer_record_disable(struct ring_buffer *buffer);
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void ring_buffer_record_enable(struct ring_buffer *buffer);
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void ring_buffer_record_off(struct ring_buffer *buffer);
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void ring_buffer_record_on(struct ring_buffer *buffer);
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bool ring_buffer_record_is_on(struct ring_buffer *buffer);
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bool ring_buffer_record_is_set_on(struct ring_buffer *buffer);
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void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu);
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void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu);
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u64 ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_bytes_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_entries(struct ring_buffer *buffer);
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unsigned long ring_buffer_overruns(struct ring_buffer *buffer);
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unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu);
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unsigned long ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu);
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u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu);
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void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
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int cpu, u64 *ts);
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void ring_buffer_set_clock(struct ring_buffer *buffer,
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u64 (*clock)(void));
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void ring_buffer_set_time_stamp_abs(struct ring_buffer *buffer, bool abs);
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bool ring_buffer_time_stamp_abs(struct ring_buffer *buffer);
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size_t ring_buffer_nr_pages(struct ring_buffer *buffer, int cpu);
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size_t ring_buffer_nr_dirty_pages(struct ring_buffer *buffer, int cpu);
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void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu);
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void ring_buffer_free_read_page(struct ring_buffer *buffer, int cpu, void *data);
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int ring_buffer_read_page(struct ring_buffer *buffer, void **data_page,
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size_t len, int cpu, int full);
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struct trace_seq;
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int ring_buffer_print_entry_header(struct trace_seq *s);
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int ring_buffer_print_page_header(struct trace_seq *s);
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enum ring_buffer_flags {
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RB_FL_OVERWRITE = 1 << 0,
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};
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#ifdef CONFIG_RING_BUFFER
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int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node);
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#else
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#define trace_rb_cpu_prepare NULL
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#endif
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#endif /* _LINUX_RING_BUFFER_H */
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