Re: [PATCH] io_uring/register: guard compat syscall with CONFIG_COMPAT

[Jeff Moyer <jmoyer@redhat.com>]

Jens Axboe <axboe@kernel.dk> writes:

> On 1/17/24 8:59 AM, Jeff Moyer wrote:
>> Hi, Jens,
>> 
>> Jens Axboe <axboe@kernel.dk> writes:
>> 
>>> Add compat.h include to avoid a potential build issue:
>>>
>>> io_uring/register.c:281:6: error: call to undeclared function 'in_compat_syscall'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
>>>
>>> if (in_compat_syscall()) {
>>>     ^
>>> 1 warning generated.
>>> io_uring/register.c:282:9: error: call to undeclared function 'compat_get_bitmap'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
>>> ret = compat_get_bitmap(cpumask_bits(new_mask),
>>>       ^
>>>
>>> Fixes: c43203154d8a ("io_uring/register: move io_uring_register(2) related code to register.c")
>>> Reported-by: Manu Bretelle <chantra@meta.com>
>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>>
>>> ---
>>>
>>> diff --git a/io_uring/register.c b/io_uring/register.c
>>> index 708dd1d89add..5e62c1208996 100644
>>> --- a/io_uring/register.c
>>> +++ b/io_uring/register.c
>>> @@ -14,6 +14,7 @@
>>>  #include <linux/slab.h>
>>>  #include <linux/uaccess.h>
>>>  #include <linux/nospec.h>
>>> +#include <linux/compat.h>
>>>  #include <linux/io_uring.h>
>>>  #include <linux/io_uring_types.h>
>> 
>> This makes sense to me, but I wasn't able to reproduce that build error
>> after disabling CONFIG_COMPAT.
>
> I couldn't either, but apparently it happened internally with our kdump
> config variant.

ok.

>>> @@ -278,13 +279,14 @@ static __cold int io_register_iowq_aff(struct io_ring_ctx *ctx,
>>>  	if (len > cpumask_size())
>>>  		len = cpumask_size();
>>>  
>>> -	if (in_compat_syscall()) {
>>> +#ifdef CONFIG_COMPAT
>>> +	if (in_compat_syscall())
>> 
>> I don't think this is needed.
>> 
>> linux/compat.h:
>> ...
>> #else /* !CONFIG_COMPAT */
>> 
>> #define is_compat_task() (0)
>> /* Ensure no one redefines in_compat_syscall() under !CONFIG_COMPAT */
>> #define in_compat_syscall in_compat_syscall
>> static inline bool in_compat_syscall(void) { return false; }
>> 
>> Isn't the code fine as-is?
>
> It probably is, but this makes it consistent with the other spots we do
> compat handling. Hence I'd prefer to keep it like that, and then perhaps
> we can prune them all at some point.

I see one other spot.  :)  But if you are happy with it, that's fine by
me.

> Thanks for taking a look!

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

Cheers,
Jeff