io_uring: Ensure mask is initialized in io_arm_poll_handler

Clang warns:

fs/io_uring.c:4178:6: warning: variable 'mask' is used uninitialized
whenever 'if' condition is false [-Wsometimes-uninitialized]
        if (def->pollin)
            ^~~~~~~~~~~
fs/io_uring.c:4182:2: note: uninitialized use occurs here
        mask |= POLLERR | POLLPRI;
        ^~~~
fs/io_uring.c:4178:2: note: remove the 'if' if its condition is always
true
        if (def->pollin)
        ^~~~~~~~~~~~~~~~
fs/io_uring.c:4154:15: note: initialize the variable 'mask' to silence
this warning
        __poll_t mask, ret;
                     ^
                      = 0
1 warning generated.

io_op_defs has many definitions where pollin is not set so mask indeed
might be uninitialized. Initialize it to zero and change the next
assignment to |=, in case further masks are added in the future to avoid
missing changing the assignment then.

Fixes: d7718a9d ("io_uring: use poll driven retry for files that support it")
Link: https://github.com/ClangBuiltLinux/linux/issues/916Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -3738,8 +3738,9 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
 	req->apoll = apoll;
 	INIT_HLIST_NODE(&req->hash_node);
 
+	mask = 0;
 	if (def->pollin)
-		mask = POLLIN | POLLRDNORM;
+		mask |= POLLIN | POLLRDNORM;
 	if (def->pollout)
 		mask |= POLLOUT | POLLWRNORM;
 	mask |= POLLERR | POLLPRI;