Documentation/atomic_ops.txt (182dd4b277177e8465ad11cd9f85f282946b5578) says that pointers, longs, ints, and chars are stored and loaded atomically.
But GCC actually may split assignment to 'long' variable into two instructions. see example in http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55981 GCC also splits assignments to 'volatile' variables and this is actually a bug in gcc. volatile unsigned long y; y = 0x100000001ul; 400728: c7 05 66 06 20 00 01 movl $0x1,0x200666(%rip) # 600d98 <y> 40072f: 00 00 00 400732: c7 05 60 06 20 00 01 movl $0x1,0x200660(%rip) # 600d9c <y+0x4> 400739: 00 00 00 fortunately for y = 0; it generates this: 40071d: 48 c7 05 70 06 20 00 movq $0x0,0x200670(%rip) # 600d98 <y> 400724: 00 00 00 00 Thus NULL is safe, but constant ERR_PTR may be dangerous. Probably rcu_assign_pointer() should use ACCESS_ONCE() around lvalue, because splitting assignment for non-volatile variable seems like completely valid, but this may help only after fixing that bug in GCC. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
