linux-kernel - [tip:core/urgent] stacktrace: Unbreak stack_trace_save_tsk

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Message-ID: <tip-7eaf51a2e094229b75cc0c315f1cbbe2f3960058@git.kernel.org>
Date:   Sun, 19 May 2019 02:46:25 -0700
From:   tip-bot for Joe Lawrence <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, tglx@...utronix.de, kamalesh@...ux.vnet.ibm.com,
        linux-kernel@...r.kernel.org, joe.lawrence@...hat.com,
        hpa@...or.com, jpoimboe@...hat.com, mbenes@...e.cz
Subject: [tip:core/urgent] stacktrace: Unbreak
 stack_trace_save_tsk_reliable()

Commit-ID:  7eaf51a2e094229b75cc0c315f1cbbe2f3960058
Gitweb:     https://git.kernel.org/tip/7eaf51a2e094229b75cc0c315f1cbbe2f3960058
Author:     Joe Lawrence <joe.lawrence@...hat.com>
AuthorDate: Fri, 17 May 2019 14:51:17 -0400
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Sun, 19 May 2019 11:43:22 +0200

stacktrace: Unbreak stack_trace_save_tsk_reliable()

Miroslav reported that the livepatch self-tests were failing, specifically
a case in which the consistency model ensures that a current executing
function is not allowed to be patched, "TEST: busy target module".

Recent renovations of stack_trace_save_tsk_reliable() left it returning
only an -ERRNO success indication in some configuration combinations:

  klp_check_stack()
    ret = stack_trace_save_tsk_reliable()
      #ifdef CONFIG_ARCH_STACKWALK && CONFIG_HAVE_RELIABLE_STACKTRACE
        stack_trace_save_tsk_reliable()
          ret = arch_stack_walk_reliable()
            return 0
            return -EINVAL
          ...
          return ret;
    ...
    if (ret < 0)
      /* stack_trace_save_tsk_reliable error */
    nr_entries = ret;                               << 0

Previously (and currently for !CONFIG_ARCH_STACKWALK &&
CONFIG_HAVE_RELIABLE_STACKTRACE) stack_trace_save_tsk_reliable() returned
the number of entries that it consumed in the passed storage array.

In the case of the above config and trace, be sure to return the
stacktrace_cookie.len on stack_trace_save_tsk_reliable() success.

Fixes: 25e39e32b0a3f ("livepatch: Simplify stack trace retrieval")
Reported-by: Miroslav Benes <mbenes@...e.cz>
Signed-off-by: Joe Lawrence <joe.lawrence@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: live-patching@...r.kernel.org
Cc: jikos@...nel.org
Cc: pmladek@...e.com
Link: https://lkml.kernel.org/r/20190517185117.24642-1-joe.lawrence@redhat.com

---
 kernel/stacktrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 27bafc1e271e..90d3e0bf0302 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -206,7 +206,7 @@ int stack_trace_save_tsk_reliable(struct task_struct *tsk, unsigned long *store,
 
 	ret = arch_stack_walk_reliable(consume_entry, &c, tsk);
 	put_task_stack(tsk);
-	return ret;
+	return ret ? ret : c.len;
 }
 #endif