On 01/14/2013 11:26 AM, Cong Ding wrote:
> the variable backup_current_thread_info isn't freed before existing the
> function.
>
> Signed-off-by: Cong Ding <ding...@gmail.com>
> ---
> arch/powerpc/kernel/kgdb.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
> index 8747447..5ca82cd 100644
> --- a/arch/powerpc/kernel/kgdb.c
> +++ b/arch/powerpc/kernel/kgdb.c
> @@ -154,12 +154,12 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
> static int kgdb_singlestep(struct pt_regs *regs)
> {
> struct thread_info *thread_info, *exception_thread_info;
> - struct thread_info *backup_current_thread_info = \
> - (struct thread_info *)kmalloc(sizeof(struct thread_info),
> GFP_KERNEL);
> + struct thread_info *backup_current_thread_info;
Woh... This is definitely wrong. You have found a problem for sure,
but this is not the right way to fix it.
It is not a good idea to kmalloc while single stepping because you can
hang the kernel if you single step any operation in kmalloc().
I am in the process of going through all the kgdb mails from the last
few months while I had been away from the project, so I didn't catch
this one and I see it has upstream commit (fefd9e6f8). I'll submit
another patch to fix this the right way and use a static variable.
This is ok to use a static variable here because this is not something
we can recursively call at a single CPU level.
If Ben prefers we not burn the memory unless kgdb is active we can
kmalloc / kfree the space we need at the time that kgdb is
initialized. Else we can go with this patch you see below. We'll see
what Ben desires.
-----
diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index a7bc752..bb12c8b 100644
--- a/arch/powerpc/kernel/kgdb.c
+++ b/arch/powerpc/kernel/kgdb.c
@@ -151,15 +151,16 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
return 1;
}
+static struct thread_info kgdb_backup_thread_info[NR_CPUS];
+
static int kgdb_singlestep(struct pt_regs *regs)
{
struct thread_info *thread_info, *exception_thread_info;
- struct thread_info *backup_current_thread_info;
+ int cpu = raw_smp_processor_id();
if (user_mode(regs))
return 0;
- backup_current_thread_info = (struct thread_info
*)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
/*
* On Book E and perhaps other processors, singlestep is handled on
* the critical exception stack. This causes current_thread_info()
@@ -175,7 +176,7 @@ static int kgdb_singlestep(struct pt_regs *regs)
if (thread_info != exception_thread_info) {
/* Save the original current_thread_info. */
- memcpy(backup_current_thread_info, exception_thread_info,
sizeof *thread_info);
+ memcpy(&kgdb_backup_thread_info[cpu], exception_thread_info,
sizeof *thread_info);
memcpy(exception_thread_info, thread_info, sizeof *thread_info);
}
@@ -183,9 +184,8 @@ static int kgdb_singlestep(struct pt_regs *regs)
if (thread_info != exception_thread_info)
/* Restore current_thread_info lastly. */
- memcpy(exception_thread_info, backup_current_thread_info,
sizeof *thread_info);
+ memcpy(exception_thread_info, &kgdb_backup_thread_info[cpu],
sizeof *thread_info);
- kfree(backup_current_thread_info);
return 1;
}
-----
Thanks,
Jason.
>
> if (user_mode(regs))
> return 0;
>
> + backup_current_thread_info = (struct thread_info
> *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
> /*
> * On Book E and perhaps other processors, singlestep is handled on
> * the critical exception stack. This causes current_thread_info()
> @@ -185,6 +185,7 @@ static int kgdb_singlestep(struct pt_regs *regs)
> /* Restore current_thread_info lastly. */
> memcpy(exception_thread_info, backup_current_thread_info,
> sizeof *thread_info);
>
> + kfree(backup_current_thread_info);
> return 1;
> }
>
>
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