On Mon, Oct 31, 2022 at 10:26:21PM +0800, Gaosheng Cui wrote: > Shifting signed 32-bit value by 31 bits is undefined, so changing most > significant bit to unsigned, and mark all of the flags as unsigned so > that we don't mix types. The UBSAN warning calltrace like below: ... is completely irrelevant. If you want to credit UBSAN for finding that - sure, no problem, but who cares about the call chain leading to use of SB_NOUSER? If nothing else, report would be just as valid if the only use had been in initializer for static variable... I've no problem with the change itself, but I'd go with something along the lines of ---- SB_... flags are masks for struct super_block ->s_flags, which is an unsigned long. In particular, SB_NOUSER lives in bit 31. 1 << 31 is not the right way to spell that - it's not just that it is an undefined behaviour; it's not the right value when used to initialize an unsigned long variable. Nasal demons aside, on 64bit architecture unsigned long v = 1 << 31; is *not* going to have v equal to 0x80000000 - it'll be 0xffffffff80000000. Make the entire bunch explicitly unsigned - 1U << constant. Note that it doesn't make sense to go for 1UL - the flags are arch-independent and that limits us to 32 bits anyway. Spotted by UBSAN. ---- for commit message. Not sure about "Fixes:", to be honest...
