lkml.org 
[lkml]   [2016]   [Apr]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.4 166/210] tracing: Fix trace_printk() to print when not using bprintk()
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Steven Rostedt (Red Hat) <rostedt@goodmis.org>

    commit 3debb0a9ddb16526de8b456491b7db60114f7b5e upstream.

    The trace_printk() code will allocate extra buffers if the compile detects
    that a trace_printk() is used. To do this, the format of the trace_printk()
    is saved to the __trace_printk_fmt section, and if that section is bigger
    than zero, the buffers are allocated (along with a message that this has
    happened).

    If trace_printk() uses a format that is not a constant, and thus something
    not guaranteed to be around when the print happens, the compiler optimizes
    the fmt out, as it is not used, and the __trace_printk_fmt section is not
    filled. This means the kernel will not allocate the special buffers needed
    for the trace_printk() and the trace_printk() will not write anything to the
    tracing buffer.

    Adding a "__used" to the variable in the __trace_printk_fmt section will
    keep it around, even though it is set to NULL. This will keep the string
    from being printed in the debugfs/tracing/printk_formats section as it is
    not needed.

    Reported-by: Vlastimil Babka <vbabka@suse.cz>
    Fixes: 07d777fe8c398 "tracing: Add percpu buffers for trace_printk()"
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    include/linux/kernel.h | 6 +++---
    kernel/trace/trace_printk.c | 3 +++
    2 files changed, 6 insertions(+), 3 deletions(-)

    --- a/include/linux/kernel.h
    +++ b/include/linux/kernel.h
    @@ -607,7 +607,7 @@ do { \

    #define do_trace_printk(fmt, args...) \
    do { \
    - static const char *trace_printk_fmt \
    + static const char *trace_printk_fmt __used \
    __attribute__((section("__trace_printk_fmt"))) = \
    __builtin_constant_p(fmt) ? fmt : NULL; \
    \
    @@ -651,7 +651,7 @@ int __trace_printk(unsigned long ip, con
    */

    #define trace_puts(str) ({ \
    - static const char *trace_printk_fmt \
    + static const char *trace_printk_fmt __used \
    __attribute__((section("__trace_printk_fmt"))) = \
    __builtin_constant_p(str) ? str : NULL; \
    \
    @@ -673,7 +673,7 @@ extern void trace_dump_stack(int skip);
    #define ftrace_vprintk(fmt, vargs) \
    do { \
    if (__builtin_constant_p(fmt)) { \
    - static const char *trace_printk_fmt \
    + static const char *trace_printk_fmt __used \
    __attribute__((section("__trace_printk_fmt"))) = \
    __builtin_constant_p(fmt) ? fmt : NULL; \
    \
    --- a/kernel/trace/trace_printk.c
    +++ b/kernel/trace/trace_printk.c
    @@ -296,6 +296,9 @@ static int t_show(struct seq_file *m, vo
    const char *str = *fmt;
    int i;

    + if (!*fmt)
    + return 0;
    +
    seq_printf(m, "0x%lx : \"", *(unsigned long *)fmt);

    /*

    \
     
     \ /
      Last update: 2016-04-10 21:21    [W:2.267 / U:0.268 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site