linux-kernel - [021/156] tracing: Fix warning in s

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Message-Id: <20100330224733.571179411@linux.site>
Date:	Tue, 30 Mar 2010 15:40:55 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [021/156] tracing: Fix warning in s_next of trace file ops

2.6.33-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Lai Jiangshan <laijs@...fujitsu.com>

commit ac91d85456372a90af5b85eb6620fd2efb1e431b upstream.

This warning in s_next() can be triggered by lseek():
 [<c018b3f7>] ? s_next+0x77/0x80
 [<c013e3c1>] warn_slowpath_common+0x81/0xa0
 [<c018b3f7>] ? s_next+0x77/0x80
 [<c013e3fa>] warn_slowpath_null+0x1a/0x20
 [<c018b3f7>] s_next+0x77/0x80
 [<c01efa77>] traverse+0x117/0x200
 [<c01eff13>] seq_lseek+0xa3/0x120
 [<c01efe70>] ? seq_lseek+0x0/0x120
 [<c01d7081>] vfs_llseek+0x41/0x50
 [<c01d8116>] sys_llseek+0x66/0xa0
 [<c0102bd0>] sysenter_do_call+0x12/0x26

The iterator "leftover" variable is zeroed in the opening of the trace
file. But lseek can call s_start() which will call s_next() without
reseting the "leftover" variable back to zero, which might trigger
the WARN_ON_ONCE(iter->leftover) that is in s_next().

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
LKML-Reference: <4B8CE06A.9090207@...fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 kernel/trace/trace.c |    1 +
 1 file changed, 1 insertion(+)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1628,6 +1628,7 @@ static void *s_start(struct seq_file *m,
 
 		ftrace_enable_cpu();
 
+		iter->leftover = 0;
 		for (p = iter; p && l < *pos; p = s_next(m, p, &l))
 			;
 


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