Documentation/locking/robust-futex-ABI.rst

43 consisting of three words.  Each word is 32 bits on 32 bit arch's, or 64
55   The first word in the memory structure at 'head' contains a
60   The second word, called 'offset', specifies the offset from the
62   be called the 'lock word', from that 'lock entry'.  The 'lock word'
63   is always a 32 bit word, unlike the other words above.  The 'lock
64   word' holds 2 flag bits in the upper 2 bits, and the thread id (TID)
68   The third word, called 'list_op_pending', contains transient copy of
74 of just a single word, pointing to the next 'lock entry', or back to
77 word, is one 'lock word'.
79 The 'lock word' is always 32 bits, and is intended to be the same 32 bit
83 mechanism to register the address of that 'lock word' with the kernel.
87 'lock entry' on this list, with its associated 'lock word' at the
105 long as the 'offset' to the 'lock word' is the same for all
131 TID in the lower 30 bits of the 'lock word'.
141  1) set the 'list_op_pending' word to the address of the 'lock entry'
145     of the 'lock word', to the linked list starting at 'head', and
146  4) clear the 'list_op_pending' word.
150  1) set the 'list_op_pending' word to the address of the 'lock entry'
154  4) clear the 'lock_op_pending' word.
157 'list_op_pending' and the address of each 'lock word' found by walking
159 bits of the 'lock word' at offset 'offset' from that address equals the
162  1) if bit 31 (0x80000000) is set in that word, then attempt a futex
165  2) atomically set  bit 30 (0x40000000) in the 'lock word'.
175     is not a valid address of a user space word
176  2) the calculated location of the 'lock word' (address plus
178     word
182 When the kernel sees a list entry whose 'lock word' doesn't have the