Re: [PATCH 1/1] MdeModulePkg/UefiBootManagerLib: limit recursive call depth

[Laszlo Ersek <lersek@redhat.com>]

On 02/26/18 09:29, Heyi Guo wrote:
> Function BmRepairAllControllers may recursively call itself if some
> driver health protocol returns EfiDriverHealthStatusReconnectRequired.
> However, driver health protocol of some buggy third party driver may
> always return such status even after one and another reconnect. The
> endless iteration will cause stack overflow and then system exception,
> and it may be not easy to find that the exception is actually caused
> by stack overflow.
> 
> So we limit the number of reconnect retry to 10 to improve code
> robustness.

Not really my place to comment on this, but how about removing the
recursion entirely, and turning the logic into a normal (iterative) loop
instead?

(1) Rename the current function to:

STATIC
VOID
BmRepairAllControllersWorker (
  OUT BOOLEAN *ReconnectRequired,
  OUT BOOLEAN *RebootRequired
  );


(2) The worker function should end right before

  if (ReconnectRequired) {
    BmRepairAllControllers ();
  }


(3) The worker function should not contain

  RebootRequired    = FALSE;
  ReconnectRequired = FALSE;

Such initialization should be left to the caller.


(4) The worker function should be called in a loop from a new
BmRepairAllControllers() function, like this:

  Reconnect = 0;
  RebootRequired = FALSE;
  do {
    ReconnectRequired = FALSE;
    BmRepairAllControllersWorker (&ReconnectRequired, &RebootRequired);
    ++Reconnect;
  } while (ReconnectRequired && Reconnect < MAX_RECONNECT_REPAIR);

  DEBUG_CODE (...);

  if (RebootRequired) {
    ...
  }


In addition to eliminating the shoddy recursive call (and the shoddier
global counter, ewww :) ), this would fix the following other warts with
the code:

- When a nested call chain is unwound, we currently dump a series of
"driver health info" lists (assuming no reboot is required), in the
DEBUG_CODE section. I would argue that we should do that only once, at
the end. (Even if we have to do it multiple times, it can be moved into
the worker function, to the end.)

- It seems to be sufficient to accumulate RebootRequired into one
variable (i.e. not multiple instances of the same local variable on the
stack) and to act upon it at the very end.


Feel free to ignore my comments -- I just think we should be moving in
the opposite direction; that is, away from recursion (especially from
recursion combined with global variables -- that's one difficult pattern
to reason about).

Thanks
Laszlo

> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Heyi Guo <heyi.guo@linaro.org>
> Cc: Star Zeng <star.zeng@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> ---
>  MdeModulePkg/Library/UefiBootManagerLib/InternalBm.h     |  6 ++++++
>  MdeModulePkg/Library/UefiBootManagerLib/BmDriverHealth.c | 17 ++++++++++++++++-
>  2 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/MdeModulePkg/Library/UefiBootManagerLib/InternalBm.h b/MdeModulePkg/Library/UefiBootManagerLib/InternalBm.h
> index 25a1d522fe84..9aa86b096525 100644
> --- a/MdeModulePkg/Library/UefiBootManagerLib/InternalBm.h
> +++ b/MdeModulePkg/Library/UefiBootManagerLib/InternalBm.h
> @@ -108,6 +108,12 @@ CHAR16 *
>  #define BM_OPTION_NAME_LEN                          sizeof ("PlatformRecovery####")
>  extern CHAR16  *mBmLoadOptionName[];
>  
> +//
> +// Maximum number of reconnect retry to repair controller; it is to limit the
> +// number of recursive call of BmRepairAllControllers.
> +//
> +#define MAX_RECONNECT_REPAIR                        10
> +
>  /**
>    Visitor function to be called by BmForEachVariable for each variable
>    in variable storage.
> diff --git a/MdeModulePkg/Library/UefiBootManagerLib/BmDriverHealth.c b/MdeModulePkg/Library/UefiBootManagerLib/BmDriverHealth.c
> index ddcee8b0676f..30d70f32af84 100644
> --- a/MdeModulePkg/Library/UefiBootManagerLib/BmDriverHealth.c
> +++ b/MdeModulePkg/Library/UefiBootManagerLib/BmDriverHealth.c
> @@ -26,6 +26,12 @@ GLOBAL_REMOVE_IF_UNREFERENCED
>      L"Reboot Required"
>      };
>  
> +//
> +// Counter of reconnect retry to repair controller; it is to limit the
> +// number of recursive call of BmRepairAllControllers.
> +//
> +STATIC UINTN mReconnectRepairCount;
> +
>  /**
>    Return the controller name.
>  
> @@ -549,7 +555,16 @@ BmRepairAllControllers (
>  
>  
>    if (ReconnectRequired) {
> -    BmRepairAllControllers ();
> +    if (mReconnectRepairCount < MAX_RECONNECT_REPAIR) {
> +      mReconnectRepairCount++;
> +      BmRepairAllControllers ();
> +    } else {
> +      DEBUG ((DEBUG_ERROR, "[%a:%d] Repair failed after %d retries.\n",
> +        __FUNCTION__, __LINE__, mReconnectRepairCount));
> +      // Reset counter so that it will not affect calling
> +      // BmRepairAllControllers() somewhere else
> +      mReconnectRepairCount = 0;
> +    }
>    }
>  
>    DEBUG_CODE (
>