On Tue, 29 Mar 2022, Hannes Reinecke wrote: > On 3/28/22 18:34, Mikulas Patocka wrote: > > Early alpha processors cannot write a single byte or short; they read 8 > > bytes, modify the value in registers and write back 8 bytes. > > > > This could cause race condition in the structure dm_io - if the fields > > flags and io_count are modified simultaneously. > > > > Fix this bug by using 32-bit flags if we are on Alpha and if we are > > compiling for a processor that doesn't have the byte-word-extension. > > > Errm. > > Seeing that those alphas could only modify 64 bit atomically, what > exactly do you gain by using 32-bit flags? > Shouldn't you be using 64-bit flags? > > Cheers, > > Hannes Alpha can modify atomically aligned 32 bits or aligned 64 bits (using the STL or STQ instruction). If it needs to modify 8 or 16 bits, it reads 64 bits (using the LDQ_U instruction), modifies the value in the register (using the INSBL and MSKBL instructions) and writes back 64 bits (using the STQ_U instruction). Using 32-bit flags is safe, because it reads them and writes them directly using the 32-bit LDL and STL instructions. Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
