[PATCH] tracing: fix warning in s_next

[PATCH] tracing: fix warning in s_next

[Lai Jiangshan]

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

It is because s_start() calls s_next() without reset leftover.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
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)
 
 		ftrace_enable_cpu();
 
+		iter->leftover = 0;
 		for (p = iter; p && l < *pos; p = s_next(m, p, &l))
 			;
 

Re: [PATCH] tracing: fix warning in s_next

[Steven Rostedt]

On Tue, 2010-03-02 at 17:54 +0800, Lai Jiangshan wrote:
> 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
> 
> It is because s_start() calls s_next() without reset leftover.

Applied, Thanks!

-- Steve

> 
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> 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)
>  
>  		ftrace_enable_cpu();
>  
> +		iter->leftover = 0;
>  		for (p = iter; p && l < *pos; p = s_next(m, p, &l))
>  			;
>  

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

[tip-bot for Lai Jiangshan]

Commit-ID:  ac91d85456372a90af5b85eb6620fd2efb1e431b
Gitweb:     http://git.kernel.org/tip/ac91d85456372a90af5b85eb6620fd2efb1e431b
Author:     Lai Jiangshan <laijs@cn.fujitsu.com>
AuthorDate: Tue, 2 Mar 2010 17:54:50 +0800
Committer:  Steven Rostedt <rostedt@goodmis.org>
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@kernel.org
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4B8CE06A.9090207@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 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)
 
 		ftrace_enable_cpu();
 
+		iter->leftover = 0;
 		for (p = iter; p && l < *pos; p = s_next(m, p, &l))
 			;