Memory system and method for controlling non-volatile memory

A method for controlling a non-volatile memory, the method comprising:

• executing a first decoding process of reading data from the non-volatile memory and repeatedly executing bounded distance decoding on a plurality of symbol groups protected by each of component codes included in a plurality of component code groups, the non-volatile memory storing the data encoded by a plurality of error correction codes in which each of the plurality of symbol groups is protected by the plurality of component code groups, the data encoded by the error correction codes;
• executing a second decoding process of repeatedly executing decoding that exceeds a bounded distance in units of component codes for error symbol groups, the error symbol group determined to include an error due to a syndrome of component codes included in the plurality of component code groups when the first decoding process fails;
• executing a rollback process of returning to data before the execution of the second decoding process when the first decoding process executed after the second decoding process fails;
• and
• changing a parameter used in the second decoding process and further executing the second decoding process using the changed parameter when detecting that the second decoding process is not progressed.