Follow-up to 880e40b187aa, which added a BUG_ON() guard in read_file().

But as Jan pointed out, before ExitBootServices BUG_ON()
is not functional. It results in a hang with no message.

On the other hand blexit() prints a message and returns back
to the bootloader.

Fixes: 880e40b187aa ("xen/efi: Fix boot from a device without a file system")
Reported-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Szymon Acedański <accek@invisiblethingslab.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
Changes in v2:
- Drop the Link: tag; use Reported-by: and Fixes: instead. (Jan)

blexit() has been chosen over PrintErrMesg(), as the latter
is predominantly used in cases where an EFI call fails
(and it prints the status).

 xen/common/efi/boot.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
index 2971ea8696d1..8f24df9bc23a 100644
--- a/xen/common/efi/boot.c
+++ b/xen/common/efi/boot.c
@@ -849,7 +849,8 @@ static bool __init read_file(EFI_FILE_HANDLE dir_handle, CHAR16 *name,
     if ( !name )
         PrintErrMesg(L"No filename", EFI_OUT_OF_RESOURCES);
 
-    BUG_ON(!dir_handle);
+    if ( !dir_handle )
+        blexit(L"BUG: !dir_handle in read_file()");
 
     what = L"Open";
     ret = dir_handle->Open(dir_handle, &FileHandle, name,
-- 
2.53.0

On 6/2/26 3:17 PM, Szymon Acedański wrote:
> Follow-up to 880e40b187aa, which added a BUG_ON() guard in read_file().
> 
> But as Jan pointed out, before ExitBootServices BUG_ON()
> is not functional. It results in a hang with no message.
> 
> On the other hand blexit() prints a message and returns back
> to the bootloader.
> 
> Fixes: 880e40b187aa ("xen/efi: Fix boot from a device without a file system")
> Reported-by: Jan Beulich <jbeulich@suse.com>
> Signed-off-by: Szymon Acedański <accek@invisiblethingslab.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>

Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

Thanks.

~ Oleksii

On Tue, Jun 02, 2026 at 03:17:37PM +0200, Szymon Acedański wrote:
> Follow-up to 880e40b187aa, which added a BUG_ON() guard in read_file().
> 
> But as Jan pointed out, before ExitBootServices BUG_ON()
> is not functional. It results in a hang with no message.
> 
> On the other hand blexit() prints a message and returns back
> to the bootloader.
> 
> Fixes: 880e40b187aa ("xen/efi: Fix boot from a device without a file system")
> Reported-by: Jan Beulich <jbeulich@suse.com>
> Signed-off-by: Szymon Acedański <accek@invisiblethingslab.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

> ---
> Changes in v2:
> - Drop the Link: tag; use Reported-by: and Fixes: instead. (Jan)
> 
> blexit() has been chosen over PrintErrMesg(), as the latter
> is predominantly used in cases where an EFI call fails
> (and it prints the status).
> 
>  xen/common/efi/boot.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
> index 2971ea8696d1..8f24df9bc23a 100644
> --- a/xen/common/efi/boot.c
> +++ b/xen/common/efi/boot.c
> @@ -849,7 +849,8 @@ static bool __init read_file(EFI_FILE_HANDLE dir_handle, CHAR16 *name,
>      if ( !name )
>          PrintErrMesg(L"No filename", EFI_OUT_OF_RESOURCES);
>  
> -    BUG_ON(!dir_handle);
> +    if ( !dir_handle )
> +        blexit(L"BUG: !dir_handle in read_file()");
>  
>      what = L"Open";
>      ret = dir_handle->Open(dir_handle, &FileHandle, name,
> -- 
> 2.53.0
> 
> 

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab