linux-kernel - [tip:perf/core] uprobes: Change prepare_uretprobe() to (try to) flush the dead frames

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Date:	Fri, 31 Jul 2015 07:00:29 -0700
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	luto@...capital.net, mingo@...nel.org, panand@...hat.com,
	peterz@...radead.org, hpa@...or.com, srikar@...ux.vnet.ibm.com,
	oleg@...hat.com, arapov@...il.com, torvalds@...ux-foundation.org,
	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: [tip:perf/core] uprobes: Change prepare_uretprobe() to (try to)
  flush the dead frames

Commit-ID:  a5b7e1a89b820f2b9b23634ca4c59b555e8d9a0d
Gitweb:     http://git.kernel.org/tip/a5b7e1a89b820f2b9b23634ca4c59b555e8d9a0d
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Tue, 21 Jul 2015 15:40:23 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 31 Jul 2015 10:38:05 +0200

uprobes: Change prepare_uretprobe() to (try to) flush the dead frames

Change prepare_uretprobe() to flush the !arch_uretprobe_is_alive()
return_instance's. This is not needed correctness-wise, but can help
to avoid the failure caused by MAX_URETPROBE_DEPTH.

Note: in this case arch_uretprobe_is_alive() can be false
positive, the stack can grow after longjmp(). Unfortunately, the
kernel can't 100% solve this problem, but see the next patch.

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/20150721134023.GA4776@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/events/uprobes.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 93d939c8..7e61c8c 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1511,6 +1511,16 @@ static unsigned long get_trampoline_vaddr(void)
 	return trampoline_vaddr;
 }
 
+static void cleanup_return_instances(struct uprobe_task *utask, struct pt_regs *regs)
+{
+	struct return_instance *ri = utask->return_instances;
+	while (ri && !arch_uretprobe_is_alive(ri, regs)) {
+		ri = free_ret_instance(ri);
+		utask->depth--;
+	}
+	utask->return_instances = ri;
+}
+
 static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
 {
 	struct return_instance *ri;
@@ -1541,6 +1551,9 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
 	if (orig_ret_vaddr == -1)
 		goto fail;
 
+	/* drop the entries invalidated by longjmp() */
+	cleanup_return_instances(utask, regs);
+
 	/*
 	 * We don't want to keep trampoline address in stack, rather keep the
 	 * original return address of first caller thru all the consequent
--
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