Re: [PATCH 5.10.y] mptcp: fix sometimes-uninitialized warning

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Sep 30, 2024 at 06:23:46PM +0200, Matthieu Baerts (NGI0) wrote:
> Nathan reported this issue:
> 
>   $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 LLVM_IAS=1 mrproper allmodconfig net/mptcp/subflow.o
>   net/mptcp/subflow.c:877:6: warning: variable 'incr' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
>     877 |         if (WARN_ON_ONCE(offset > skb->len))
>         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   include/asm-generic/bug.h:101:33: note: expanded from macro 'WARN_ON_ONCE'
>     101 | #define WARN_ON_ONCE(condition) ({                              \
>         |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     102 |         int __ret_warn_on = !!(condition);                      \
>         |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     103 |         if (unlikely(__ret_warn_on))                            \
>         |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     104 |                 __WARN_FLAGS(BUGFLAG_ONCE |                     \
>         |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     105 |                              BUGFLAG_TAINT(TAINT_WARN));        \
>         |                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     106 |         unlikely(__ret_warn_on);                                \
>         |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     107 | })
>         | ~~
>   net/mptcp/subflow.c:893:6: note: uninitialized use occurs here
>     893 |         if (incr)
>         |             ^~~~
>   net/mptcp/subflow.c:877:2: note: remove the 'if' if its condition is always false
>     877 |         if (WARN_ON_ONCE(offset > skb->len))
>         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     878 |                 goto out;
>         |                 ~~~~~~~~
>   net/mptcp/subflow.c:874:18: note: initialize the variable 'incr' to silence this warning
>     874 |         u32 offset, incr, avail_len;
>         |                         ^
>         |                          = 0
>   1 warning generated.
> 
> As mentioned by Nathan, this issue is present because 5.10 does not
> include commit ea4ca586b16f ("mptcp: refine MPTCP-level ack scheduling"),
> which removed the use of 'incr' in the error path added by this change.
> This other commit does not really look suitable for stable, hence this
> dedicated patch for 5.10.
> 
> Fixes: e93fa44f0714 ("mptcp: fix duplicate data handling")
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Closes: https://lore.kernel.org/20240928175524.GA1713144@thelio-3990X
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> ---
>  net/mptcp/subflow.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Now applied, thanks!

greg k-h