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Commit f55fc2a5 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf: Restructure perf syscall point of no return 



The exclusive_event_installable() stuff only works because its
exclusive with the grouping bits.

Rework the code such that there is a sane place to error out before we
go do things we cannot undo.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent dfe1f3cb

kernel/events/core.c

+32 −17
Original line number Diff line number Diff line
@@ -8297,13 +8297,30 @@ SYSCALL_DEFINE5(perf_event_open, 


	if (move_group) {

		gctx = group_leader->ctx;

		mutex_lock_double(&gctx->mutex, &ctx->mutex);

	} else {

		mutex_lock(&ctx->mutex);

	}



	/*

	 * Must be under the same ctx::mutex as perf_install_in_context(),

	 * because we need to serialize with concurrent event creation.

	 */

	if (!exclusive_event_installable(event, ctx)) {

		/* exclusive and group stuff are assumed mutually exclusive */

		WARN_ON_ONCE(move_group);



		err = -EBUSY;

		goto err_locked;

	}



	WARN_ON_ONCE(ctx->parent_ctx);



	if (move_group) {

		/*

		 * See perf_event_ctx_lock() for comments on the details

		 * of swizzling perf_event::ctx.

		 */

		mutex_lock_double(&gctx->mutex, &ctx->mutex);



		perf_remove_from_context(group_leader, false);



		list_for_each_entry(sibling, &group_leader->sibling_list,
@@ -8311,13 +8328,7 @@ SYSCALL_DEFINE5(perf_event_open, 
			perf_remove_from_context(sibling, false);

			put_ctx(gctx);

		}

	} else {

		mutex_lock(&ctx->mutex);

	}



	WARN_ON_ONCE(ctx->parent_ctx);



	if (move_group) {

		/*

		 * Wait for everybody to stop referencing the events through

		 * the old lists, before installing it on new lists.
@@ -8349,22 +8360,20 @@ SYSCALL_DEFINE5(perf_event_open, 
		perf_event__state_init(group_leader);

		perf_install_in_context(ctx, group_leader, group_leader->cpu);

		get_ctx(ctx);

	}



	if (!exclusive_event_installable(event, ctx)) {

		err = -EBUSY;

		mutex_unlock(&ctx->mutex);

		fput(event_file);

		goto err_context;

		/*

		 * Now that all events are installed in @ctx, nothing

		 * references @gctx anymore, so drop the last reference we have

		 * on it.

		 */

		put_ctx(gctx);

	}



	perf_install_in_context(ctx, event, event->cpu);

	perf_unpin_context(ctx);



	if (move_group) {

	if (move_group)

		mutex_unlock(&gctx->mutex);

		put_ctx(gctx);

	}

	mutex_unlock(&ctx->mutex);



	put_online_cpus();
@@ -8391,6 +8400,12 @@ SYSCALL_DEFINE5(perf_event_open, 
	fd_install(event_fd, event_file);

	return event_fd;



err_locked:

	if (move_group)

		mutex_unlock(&gctx->mutex);

	mutex_unlock(&ctx->mutex);

/* err_file: */

	fput(event_file);

err_context:

	perf_unpin_context(ctx);

	put_ctx(ctx);