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SubjectRe: [PATCH] microblaze: Fix ftrace_update_ftrace_func panic
Steven J. Magnani wrote:
> The Microblaze dynamic ftrace code assumes a call ordering that is not met
> in all scenarios. Specifically, executing a command similar to:
>
> echo 105 > /sys/kernel/debug/tracing/set_ftrace_pid
>
> before any other tracing-related commands results in a kernel panic:
>
> BUG: failure at arch/microblaze/kernel/ftrace.c:198/ftrace_update_ftrace_func()!
>
> Recoding ftrace_update_ftrace_func() to use &ftrace_caller directly eliminates
> the need to capture its address elsewhere (and thus rely on a particular call
> sequence).

I would like to replicate this problem to see that there is. I am not
able to reach this fault
Please copy & paste log with your commands.

Thanks,
Michal


>
> Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
> ---
> diff -uprN a/arch/microblaze/kernel/ftrace.c b/arch/microblaze/kernel/ftrace.c
> --- a/arch/microblaze/kernel/ftrace.c 2010-04-02 13:10:54.000000000 -0500
> +++ b/arch/microblaze/kernel/ftrace.c 2010-04-02 13:13:29.000000000 -0500
> @@ -151,13 +151,10 @@ int ftrace_make_nop(struct module *mod,
> return ret;
> }
>
> -static int ret_addr; /* initialized as 0 by default */
> -
> /* I believe that first is called ftrace_make_nop before this function */
> int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> {
> int ret;
> - ret_addr = addr; /* saving where the barrier jump is */
> pr_debug("%s: addr:0x%x, rec->ip: 0x%x, imm:0x%x\n",
> __func__, (unsigned int)addr, (unsigned int)rec->ip, imm);
> ret = ftrace_modify_code(rec->ip, imm);
> @@ -194,12 +191,9 @@ int ftrace_update_ftrace_func(ftrace_fun
> ret = ftrace_modify_code(ip, upper);
> ret += ftrace_modify_code(ip + 4, lower);
>
> - /* We just need to remove the rtsd r15, 8 by NOP */
> - BUG_ON(!ret_addr);
> - if (ret_addr)
> - ret += ftrace_modify_code(ret_addr, MICROBLAZE_NOP);
> - else
> - ret = 1; /* fault */
> + /* We just need to replace the rtsd r15, 8 with NOP */
> + ret += ftrace_modify_code((unsigned long)&ftrace_caller,
> + MICROBLAZE_NOP);
>
> /* All changes are done - lets do caches consistent */
> flush_icache();
>


--
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian


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