Commit 45c815f0 authored Jan 19, 2016 by Alexander Shishkin Committed by Ingo Molnar Jan 21, 2016

perf: Synchronously free aux pages in case of allocation failure



We are currently using asynchronous deallocation in the error path in
AUX mmap code, which is unnecessary and also presents a problem for users
that wish to probe for the biggest possible buffer size they can get:
they'll get -EINVAL on all subsequent attemts to allocate a smaller
buffer before the asynchronous deallocation callback frees up the pages
from the previous unsuccessful attempt.

Currently, gdb does that for allocating AUX buffers for Intel PT traces.
More specifically, overwrite mode of AUX pmus that don't support hardware
sg (some implementations of Intel PT, for instance) is limited to only
one contiguous high order allocation for its buffer and there is no way
of knowing its size without trying.

This patch changes error path freeing to be synchronous as there won't
be any contenders for the AUX pages at that point.

Reported-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/1453216469-9509-1-git-send-email-alexander.shishkin@linux.intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 0e1eb0a1

kernel/events/ring_buffer.c

+20 −20

Original line number	Diff line number	Diff line
		@@ -459,6 +459,25 @@ static void rb_free_aux_page(struct ring_buffer *rb, int idx)
		__free_page(page);
		}

		static void __rb_free_aux(struct ring_buffer *rb)
		{
		int pg;

		if (rb->aux_priv) {
		rb->free_aux(rb->aux_priv);
		rb->free_aux = NULL;
		rb->aux_priv = NULL;
		}

		if (rb->aux_nr_pages) {
		for (pg = 0; pg < rb->aux_nr_pages; pg++)
		rb_free_aux_page(rb, pg);

		kfree(rb->aux_pages);
		rb->aux_nr_pages = 0;
		}
		}

		int rb_alloc_aux(struct ring_buffer rb, struct perf_event event,
		pgoff_t pgoff, int nr_pages, long watermark, int flags)
		{
		@@ -547,30 +566,11 @@ out:
		if (!ret)
		rb->aux_pgoff = pgoff;
		else
		rb_free_aux(rb);
		__rb_free_aux(rb);

		return ret;
		}

		static void __rb_free_aux(struct ring_buffer *rb)
		{
		int pg;

		if (rb->aux_priv) {
		rb->free_aux(rb->aux_priv);
		rb->free_aux = NULL;
		rb->aux_priv = NULL;
		}

		if (rb->aux_nr_pages) {
		for (pg = 0; pg < rb->aux_nr_pages; pg++)
		rb_free_aux_page(rb, pg);

		kfree(rb->aux_pages);
		rb->aux_nr_pages = 0;
		}
		}

		void rb_free_aux(struct ring_buffer *rb)
		{
		if (atomic_dec_and_test(&rb->aux_refcount))

Admin message