[tip:tracing/urgent] tracing: Fix warning in s_next of trace file ops

From: tip-bot for Lai Jiangshan
Date: Thu Mar 04 2010 - 11:31:15 EST

Commit-ID: ac91d85456372a90af5b85eb6620fd2efb1e431b
Gitweb: http://git.kernel.org/tip/ac91d85456372a90af5b85eb6620fd2efb1e431b
Author: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
AuthorDate: Tue, 2 Mar 2010 17:54:50 +0800
Committer: Steven Rostedt <rostedt@xxxxxxxxxxx>
CommitDate: Tue, 2 Mar 2010 21:11:47 -0500

tracing: Fix warning in s_next of trace file ops

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().

Cc: stable@xxxxxxxxxx
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
LKML-Reference: <4B8CE06A.9090207@xxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
kernel/trace/trace.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 032c57c..5edf410 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1703,6 +1703,7 @@ static void *s_start(struct seq_file *m, loff_t *pos)


+ iter->leftover = 0;
for (p = iter; p && l < *pos; p = s_next(m, p, &l))

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