linux-kernel - [tip:perf/core] uprobes: Change handle_trampoline() to find the next chain beforehand

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Date:	Fri, 31 Jul 2015 06:59:11 -0700
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	arapov@...il.com, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, srikar@...ux.vnet.ibm.com,
	oleg@...hat.com, peterz@...radead.org, mingo@...nel.org,
	tglx@...utronix.de, hpa@...or.com, luto@...capital.net,
	panand@...hat.com
Subject: [tip:perf/core] uprobes: Change handle_trampoline()
  to find the next chain beforehand

Commit-ID:  a83cfeb92132c279b20bbc8ed3cef833b0fe417e
Gitweb:     http://git.kernel.org/tip/a83cfeb92132c279b20bbc8ed3cef833b0fe417e
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Tue, 21 Jul 2015 15:40:13 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 31 Jul 2015 10:38:04 +0200

uprobes: Change handle_trampoline() to find the next chain beforehand

No functional changes, preparation.

Add the new helper, find_next_ret_chain(), which finds the first
!chained entry and returns its ->next. Yes, it is suboptimal. We
probably want to turn ->chained into ->start_of_this_chain
pointer and avoid another loop. But this needs the boring
changes in dup_utask(), so lets do this later.

Change the main loop in handle_trampoline() to unwind the stack
until ri is equal to the pointer returned by this new helper.

Tested-by: Pratyush Anand <panand@...hat.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Acked-by: Anton Arapov <arapov@...il.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20150721134013.GA4755@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/events/uprobes.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 4c941fe..98e4d97 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1766,11 +1766,22 @@ handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs)
 	up_read(&uprobe->register_rwsem);
 }
 
+static struct return_instance *find_next_ret_chain(struct return_instance *ri)
+{
+	bool chained;
+
+	do {
+		chained = ri->chained;
+		ri = ri->next;	/* can't be NULL if chained */
+	} while (chained);
+
+	return ri;
+}
+
 static void handle_trampoline(struct pt_regs *regs)
 {
 	struct uprobe_task *utask;
-	struct return_instance *ri;
-	bool chained;
+	struct return_instance *ri, *next;
 
 	utask = current->utask;
 	if (!utask)
@@ -1780,24 +1791,18 @@ static void handle_trampoline(struct pt_regs *regs)
 	if (!ri)
 		goto sigill;
 
+	next = find_next_ret_chain(ri);
 	/*
 	 * TODO: we should throw out return_instance's invalidated by
 	 * longjmp(), currently we assume that the probed function always
 	 * returns.
 	 */
 	instruction_pointer_set(regs, ri->orig_ret_vaddr);
-
-	for (;;) {
+	do {
 		handle_uretprobe_chain(ri, regs);
-
-		chained = ri->chained;
 		ri = free_ret_instance(ri);
 		utask->depth--;
-
-		if (!chained)
-			break;
-		BUG_ON(!ri);
-	}
+	} while (ri != next);
 
 	utask->return_instances = ri;
 	return;
--
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