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authorDouglas Anderson <dianders@chromium.org>2019-03-08 22:32:04 +0300
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2019-03-13 16:46:10 +0300
commit31b265b3baaf55f209229888b7ffea523ddab366 (patch)
tree7373d7b7958e3ac85ed3542464a72c692d35c0dd /include
parentcede666e2eb28dc8a680d1622fded533769f07a4 (diff)
downloadlinux-31b265b3baaf55f209229888b7ffea523ddab366.tar.xz
tracing: kdb: Fix ftdump to not sleep
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>
Diffstat (limited to 'include')
-rw-r--r--include/linux/ring_buffer.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index f1429675f252..1a40277b512c 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -128,7 +128,7 @@ ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
unsigned long *lost_events);
struct ring_buffer_iter *
-ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu);
+ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu, gfp_t flags);
void ring_buffer_read_prepare_sync(void);
void ring_buffer_read_start(struct ring_buffer_iter *iter);
void ring_buffer_read_finish(struct ring_buffer_iter *iter);