I did ghusl e janabat this evening but now I found some dry white stuff in the hair around my private parts. Before doing ghusl, I don't know if it was there on not. Is my ghusl valid?

If some fluid is discharged by a man who is not sick and that fluid has one of the three characteristics mentioned in the previous ruling, but the man does not know whether or not it had any of the other characteristics, [he will not be junub and] in the event that he had wuḍūʾ before the discharge of the fluid, that wuḍūʾ remains valid. And if he did not have wuḍūʾ, he only needs to perform wuḍūʾ [when required], and performing ghusl is not obligatory on him.

Ruling 347. It is recommended that one urinates after ejaculation; if he does not urinate, and after performing ghusl some fluid comes out about which he does not know whether it is semen or some other fluid, it is ruled as being semen.