On Tue, 29 Jul 2025 05:53:23 +0100, Al Viro wrote: >FAT12 problem is that FAT entries being accessed there are 12-bit, packed in >pairs into an array of 3-byte values. Have you actually read what the functions I learned it. I didn't really understand this code, but after your hint, I understood that the 12-bit entry FAT12 has 3 bytes, and cacheline will not be an integer multiple of 3. Finally, the entry with fat12 may exceed the judgment of cacheline. >are doing? There we *must* serialize the access to bytes that have 4 bits >from one entry and 4 from another - there's no such thing as atomically >update half a byte; it has to be read, modified and stored back. If two >threads try to do that to upper and lower halves of the same byte at the >same time, the value will be corrupted. I will change the fix to READ_ONCE/WRITE_ONCE later. BR, Edward
