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attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ,/translations/zh_CN/locking/robust-futex-ABI”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ,/translations/zh_TW/locking/robust-futex-ABI”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ,/translations/it_IT/locking/robust-futex-ABI”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ,/translations/ja_JP/locking/robust-futex-ABI”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ,/translations/ko_KR/locking/robust-futex-ABI”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒPortuguese (Brazilian)”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ,/translations/pt_BR/locking/robust-futex-ABI”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh–sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ,/translations/sp_SP/locking/robust-futex-ABI”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒThe robust futex ABI”h]”hŒThe robust futex ABI”…””}”(hh¼h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhh·h²hh³ŒF/var/lib/git/docbuild/linux/Documentation/locking/robust-futex-ABI.rst”h´KubhŒ
field_list”“”)”}”(hhh]”hŒfield”“”)”}”(hhh]”(hŒ
field_name”“”)”}”(hŒAuthor”h]”hŒAuthor”…””}”(hh×h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÕhhÒh³hÊh´K ubhŒ
field_body”“”)”}”(hŒ&Started by Paul Jackson <pj@sgi.com>

”h]”hŒ	paragraph”“”)”}”(hŒ$Started by Paul Jackson <pj@sgi.com>”h]”(hŒStarted by Paul Jackson <”…””}”(hhíh²hh³Nh´NubhŒ	reference”“”)”}”(hŒ
pj@sgi.com”h]”hŒ
pj@sgi.com”…””}”(hh÷h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefuri”Œmailto:pj@sgi.com”uh1hõhhíubhŒ>”…””}”(hhíh²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Khhçubah}”(h]”h ]”h"]”h$]”h&]”uh1håhhÒubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÐh³hÊh´KhhÍh²hubah}”(h]”h ]”h"]”h$]”h&]”uh1hËhh·h²hh³hÊh´Kubhì)”}”(hŒ‡Robust_futexes provide a mechanism that is used in addition to normal
futexes, for kernel assist of cleanup of held locks on task exit.”h]”hŒ‡Robust_futexes provide a mechanism that is used in addition to normal
futexes, for kernel assist of cleanup of held locks on task exit.”…””}”(hj#  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Khh·h²hubhì)”}”(hX;  The interesting data as to what futexes a thread is holding is kept on a
linked list in user space, where it can be updated efficiently as locks
are taken and dropped, without kernel intervention.  The only additional
kernel intervention required for robust_futexes above and beyond what is
required for futexes is:”h]”hX;  The interesting data as to what futexes a thread is holding is kept on a
linked list in user space, where it can be updated efficiently as locks
are taken and dropped, without kernel intervention.  The only additional
kernel intervention required for robust_futexes above and beyond what is
required for futexes is:”…””}”(hj1  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Khh·h²hubhŒblock_quote”“”)”}”(hŒÃ1) a one time call, per thread, to tell the kernel where its list of
   held robust_futexes begins, and
2) internal kernel code at exit, to handle any listed locks held
   by the exiting thread.
”h]”hŒenumerated_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hŒaa one time call, per thread, to tell the kernel where its list of
held robust_futexes begins, and”h]”hì)”}”(hŒaa one time call, per thread, to tell the kernel where its list of
held robust_futexes begins, and”h]”hŒaa one time call, per thread, to tell the kernel where its list of
held robust_futexes begins, and”…””}”(hjP  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´KhjL  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjG  ubjK  )”}”(hŒUinternal kernel code at exit, to handle any listed locks held
by the exiting thread.
”h]”hì)”}”(hŒTinternal kernel code at exit, to handle any listed locks held
by the exiting thread.”h]”hŒTinternal kernel code at exit, to handle any listed locks held
by the exiting thread.”…””}”(hjh  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Khjd  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjG  ubeh}”(h]”h ]”h"]”h$]”h&]”Œenumtype”Œarabic”Œprefix”hŒsuffix”Œ)”uh1jE  hjA  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j?  h³hÊh´Khh·h²hubhì)”}”(hXm  The existing normal futexes already provide a "Fast Userspace Locking"
mechanism, which handles uncontested locking without needing a system
call, and handles contested locking by maintaining a list of waiting
threads in the kernel.  Options on the sys_futex(2) system call support
waiting on a particular futex, and waking up the next waiter on a
particular futex.”h]”hXq  The existing normal futexes already provide a â€œFast Userspace Lockingâ€
mechanism, which handles uncontested locking without needing a system
call, and handles contested locking by maintaining a list of waiting
threads in the kernel.  Options on the sys_futex(2) system call support
waiting on a particular futex, and waking up the next waiter on a
particular futex.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Khh·h²hubhì)”}”(hXx  For robust_futexes to work, the user code (typically in a library such
as glibc linked with the application) has to manage and place the
necessary list elements exactly as the kernel expects them.  If it fails
to do so, then improperly listed locks will not be cleaned up on exit,
probably causing deadlock or other such failure of the other threads
waiting on the same locks.”h]”hXx  For robust_futexes to work, the user code (typically in a library such
as glibc linked with the application) has to manage and place the
necessary list elements exactly as the kernel expects them.  If it fails
to do so, then improperly listed locks will not be cleaned up on exit,
probably causing deadlock or other such failure of the other threads
waiting on the same locks.”…””}”(hj›  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Khh·h²hubhì)”}”(hŒ\A thread that anticipates possibly using robust_futexes should first
issue the system call::”h]”hŒ[A thread that anticipates possibly using robust_futexes should first
issue the system call:”…””}”(hj©  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K$hh·h²hubhŒliteral_block”“”)”}”(hŒVasmlinkage long
sys_set_robust_list(struct robust_list_head __user *head, size_t len);”h]”hŒVasmlinkage long
sys_set_robust_list(struct robust_list_head __user *head, size_t len);”…””}”hj¹  sbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1j·  h³hÊh´K'hh·h²hubhì)”}”(hŒóThe pointer 'head' points to a structure in the threads address space
consisting of three words.  Each word is 32 bits on 32 bit arch's, or 64
bits on 64 bit arch's, and local byte order.  Each thread should have
its own thread private 'head'.”h]”hŒÿThe pointer â€˜headâ€™ points to a structure in the threads address space
consisting of three words.  Each word is 32 bits on 32 bit archâ€™s, or 64
bits on 64 bit archâ€™s, and local byte order.  Each thread should have
its own thread private â€˜headâ€™.”…””}”(hjÉ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K*hh·h²hubhì)”}”(hX¼  If a thread is running in 32 bit compatibility mode on a 64 native arch
kernel, then it can actually have two such structures - one using 32 bit
words for 32 bit compatibility mode, and one using 64 bit words for 64
bit native mode.  The kernel, if it is a 64 bit kernel supporting 32 bit
compatibility mode, will attempt to process both lists on each task
exit, if the corresponding sys_set_robust_list() call has been made to
setup that list.”h]”hX¼  If a thread is running in 32 bit compatibility mode on a 64 native arch
kernel, then it can actually have two such structures - one using 32 bit
words for 32 bit compatibility mode, and one using 64 bit words for 64
bit native mode.  The kernel, if it is a 64 bit kernel supporting 32 bit
compatibility mode, will attempt to process both lists on each task
exit, if the corresponding sys_set_robust_list() call has been made to
setup that list.”…””}”(hj×  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K/hh·h²hubj@  )”}”(hXÂ  The first word in the memory structure at 'head' contains a
pointer to a single linked list of 'lock entries', one per lock,
as described below.  If the list is empty, the pointer will point
to itself, 'head'.  The last 'lock entry' points back to the 'head'.

The second word, called 'offset', specifies the offset from the
address of the associated 'lock entry', plus or minus, of what will
be called the 'lock word', from that 'lock entry'.  The 'lock word'
is always a 32 bit word, unlike the other words above.  The 'lock
word' holds 2 flag bits in the upper 2 bits, and the thread id (TID)
of the thread holding the lock in the bottom 30 bits.  See further
below for a description of the flag bits.

The third word, called 'list_op_pending', contains transient copy of
the address of the 'lock entry', during list insertion and removal,
and is needed to correctly resolve races should a thread exit while
in the middle of a locking or unlocking operation.
”h]”(hì)”}”(hX  The first word in the memory structure at 'head' contains a
pointer to a single linked list of 'lock entries', one per lock,
as described below.  If the list is empty, the pointer will point
to itself, 'head'.  The last 'lock entry' points back to the 'head'.”h]”hX  The first word in the memory structure at â€˜headâ€™ contains a
pointer to a single linked list of â€˜lock entriesâ€™, one per lock,
as described below.  If the list is empty, the pointer will point
to itself, â€˜headâ€™.  The last â€˜lock entryâ€™ points back to the â€˜headâ€™.”…””}”(hjé  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K7hjå  ubhì)”}”(hX»  The second word, called 'offset', specifies the offset from the
address of the associated 'lock entry', plus or minus, of what will
be called the 'lock word', from that 'lock entry'.  The 'lock word'
is always a 32 bit word, unlike the other words above.  The 'lock
word' holds 2 flag bits in the upper 2 bits, and the thread id (TID)
of the thread holding the lock in the bottom 30 bits.  See further
below for a description of the flag bits.”h]”hXÓ  The second word, called â€˜offsetâ€™, specifies the offset from the
address of the associated â€˜lock entryâ€™, plus or minus, of what will
be called the â€˜lock wordâ€™, from that â€˜lock entryâ€™.  The â€˜lock wordâ€™
is always a 32 bit word, unlike the other words above.  The â€˜lock
wordâ€™ holds 2 flag bits in the upper 2 bits, and the thread id (TID)
of the thread holding the lock in the bottom 30 bits.  See further
below for a description of the flag bits.”…””}”(hj÷  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K<hjå  ubhì)”}”(hŒÿThe third word, called 'list_op_pending', contains transient copy of
the address of the 'lock entry', during list insertion and removal,
and is needed to correctly resolve races should a thread exit while
in the middle of a locking or unlocking operation.”h]”hX  The third word, called â€˜list_op_pendingâ€™, contains transient copy of
the address of the â€˜lock entryâ€™, during list insertion and removal,
and is needed to correctly resolve races should a thread exit while
in the middle of a locking or unlocking operation.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´KDhjå  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j?  h³hÊh´K7hh·h²hubhì)”}”(hX3  Each 'lock entry' on the single linked list starting at 'head' consists
of just a single word, pointing to the next 'lock entry', or back to
'head' if there are no more entries.  In addition, nearby to each 'lock
entry', at an offset from the 'lock entry' specified by the 'offset'
word, is one 'lock word'.”h]”hXS  Each â€˜lock entryâ€™ on the single linked list starting at â€˜headâ€™ consists
of just a single word, pointing to the next â€˜lock entryâ€™, or back to
â€˜headâ€™ if there are no more entries.  In addition, nearby to each â€˜lock
entryâ€™, at an offset from the â€˜lock entryâ€™ specified by the â€˜offsetâ€™
word, is one â€˜lock wordâ€™.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´KIhh·h²hubhì)”}”(hX^  The 'lock word' is always 32 bits, and is intended to be the same 32 bit
lock variable used by the futex mechanism, in conjunction with
robust_futexes.  The kernel will only be able to wakeup the next thread
waiting for a lock on a threads exit if that next thread used the futex
mechanism to register the address of that 'lock word' with the kernel.”h]”hXf  The â€˜lock wordâ€™ is always 32 bits, and is intended to be the same 32 bit
lock variable used by the futex mechanism, in conjunction with
robust_futexes.  The kernel will only be able to wakeup the next thread
waiting for a lock on a threads exit if that next thread used the futex
mechanism to register the address of that â€˜lock wordâ€™ with the kernel.”…””}”(hj'  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´KOhh·h²hubhì)”}”(hX¹  For each futex lock currently held by a thread, if it wants this
robust_futex support for exit cleanup of that lock, it should have one
'lock entry' on this list, with its associated 'lock word' at the
specified 'offset'.  Should a thread die while holding any such locks,
the kernel will walk this list, mark any such locks with a bit
indicating their holder died, and wakeup the next thread waiting for
that lock using the futex mechanism.”h]”hXÅ  For each futex lock currently held by a thread, if it wants this
robust_futex support for exit cleanup of that lock, it should have one
â€˜lock entryâ€™ on this list, with its associated â€˜lock wordâ€™ at the
specified â€˜offsetâ€™.  Should a thread die while holding any such locks,
the kernel will walk this list, mark any such locks with a bit
indicating their holder died, and wakeup the next thread waiting for
that lock using the futex mechanism.”…””}”(hj5  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´KUhh·h²hubhì)”}”(hŒäWhen a thread has invoked the above system call to indicate it
anticipates using robust_futexes, the kernel stores the passed in 'head'
pointer for that task.  The task may retrieve that value later on by
using the system call::”h]”hŒçWhen a thread has invoked the above system call to indicate it
anticipates using robust_futexes, the kernel stores the passed in â€˜headâ€™
pointer for that task.  The task may retrieve that value later on by
using the system call:”…””}”(hjC  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K]hh·h²hubj¸  )”}”(hŒ„asmlinkage long
sys_get_robust_list(int pid, struct robust_list_head __user **head_ptr,
                    size_t __user *len_ptr);”h]”hŒ„asmlinkage long
sys_get_robust_list(int pid, struct robust_list_head __user **head_ptr,
                    size_t __user *len_ptr);”…””}”hjQ  sbah}”(h]”h ]”h"]”h$]”h&]”jÇ  jÈ  uh1j·  h³hÊh´Kbhh·h²hubhì)”}”(hX  It is anticipated that threads will use robust_futexes embedded in
larger, user level locking structures, one per lock.  The kernel
robust_futex mechanism doesn't care what else is in that structure, so
long as the 'offset' to the 'lock word' is the same for all
robust_futexes used by that thread.  The thread should link those locks
it currently holds using the 'lock entry' pointers.  It may also have
other links between the locks, such as the reverse side of a double
linked list, but that doesn't matter to the kernel.”h]”hX  It is anticipated that threads will use robust_futexes embedded in
larger, user level locking structures, one per lock.  The kernel
robust_futex mechanism doesnâ€™t care what else is in that structure, so
long as the â€˜offsetâ€™ to the â€˜lock wordâ€™ is the same for all
robust_futexes used by that thread.  The thread should link those locks
it currently holds using the â€˜lock entryâ€™ pointers.  It may also have
other links between the locks, such as the reverse side of a double
linked list, but that doesnâ€™t matter to the kernel.”…””}”(hj_  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Kfhh·h²hubhì)”}”(hX  By keeping its locks linked this way, on a list starting with a 'head'
pointer known to the kernel, the kernel can provide to a thread the
essential service available for robust_futexes, which is to help clean
up locks held at the time of (a perhaps unexpectedly) exit.”h]”hX  By keeping its locks linked this way, on a list starting with a â€˜headâ€™
pointer known to the kernel, the kernel can provide to a thread the
essential service available for robust_futexes, which is to help clean
up locks held at the time of (a perhaps unexpectedly) exit.”…””}”(hjm  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Kohh·h²hubhì)”}”(hXŒ  Actual locking and unlocking, during normal operations, is handled
entirely by user level code in the contending threads, and by the
existing futex mechanism to wait for, and wakeup, locks.  The kernels
only essential involvement in robust_futexes is to remember where the
list 'head' is, and to walk the list on thread exit, handling locks
still held by the departing thread, as described below.”h]”hX  Actual locking and unlocking, during normal operations, is handled
entirely by user level code in the contending threads, and by the
existing futex mechanism to wait for, and wakeup, locks.  The kernels
only essential involvement in robust_futexes is to remember where the
list â€˜headâ€™ is, and to walk the list on thread exit, handling locks
still held by the departing thread, as described below.”…””}”(hj{  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Kthh·h²hubhì)”}”(hX  There may exist thousands of futex lock structures in a threads shared
memory, on various data structures, at a given point in time. Only those
lock structures for locks currently held by that thread should be on
that thread's robust_futex linked lock list a given time.”h]”hX  There may exist thousands of futex lock structures in a threads shared
memory, on various data structures, at a given point in time. Only those
lock structures for locks currently held by that thread should be on
that threadâ€™s robust_futex linked lock list a given time.”…””}”(hj‰  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K{hh·h²hubhì)”}”(hX  A given futex lock structure in a user shared memory region may be held
at different times by any of the threads with access to that region. The
thread currently holding such a lock, if any, is marked with the threads
TID in the lower 30 bits of the 'lock word'.”h]”hX
  A given futex lock structure in a user shared memory region may be held
at different times by any of the threads with access to that region. The
thread currently holding such a lock, if any, is marked with the threads
TID in the lower 30 bits of the â€˜lock wordâ€™.”…””}”(hj—  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K€hh·h²hubhì)”}”(hXA  When adding or removing a lock from its list of held locks, in order for
the kernel to correctly handle lock cleanup regardless of when the task
exits (perhaps it gets an unexpected signal 9 in the middle of
manipulating this list), the user code must observe the following
protocol on 'lock entry' insertion and removal:”h]”hXE  When adding or removing a lock from its list of held locks, in order for
the kernel to correctly handle lock cleanup regardless of when the task
exits (perhaps it gets an unexpected signal 9 in the middle of
manipulating this list), the user code must observe the following
protocol on â€˜lock entryâ€™ insertion and removal:”…””}”(hj¥  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K…hh·h²hubhì)”}”(hŒOn insertion:”h]”hŒOn insertion:”…””}”(hj³  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K‹hh·h²hubj@  )”}”(hX   1) set the 'list_op_pending' word to the address of the 'lock entry'
   to be inserted,
2) acquire the futex lock,
3) add the lock entry, with its thread id (TID) in the bottom 30 bits
   of the 'lock word', to the linked list starting at 'head', and
4) clear the 'list_op_pending' word.
”h]”jF  )”}”(hhh]”(jK  )”}”(hŒQset the 'list_op_pending' word to the address of the 'lock entry'
to be inserted,”h]”hì)”}”(hŒQset the 'list_op_pending' word to the address of the 'lock entry'
to be inserted,”h]”hŒYset the â€˜list_op_pendingâ€™ word to the address of the â€˜lock entryâ€™
to be inserted,”…””}”(hjÌ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´KhjÈ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjÅ  ubjK  )”}”(hŒacquire the futex lock,”h]”hì)”}”(hjâ  h]”hŒacquire the futex lock,”…””}”(hjä  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Khjà  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjÅ  ubjK  )”}”(hŒadd the lock entry, with its thread id (TID) in the bottom 30 bits
of the 'lock word', to the linked list starting at 'head', and”h]”hì)”}”(hŒadd the lock entry, with its thread id (TID) in the bottom 30 bits
of the 'lock word', to the linked list starting at 'head', and”h]”hŒ‰add the lock entry, with its thread id (TID) in the bottom 30 bits
of the â€˜lock wordâ€™, to the linked list starting at â€˜headâ€™, and”…””}”(hjû  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Khj÷  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjÅ  ubjK  )”}”(hŒ"clear the 'list_op_pending' word.
”h]”hì)”}”(hŒ!clear the 'list_op_pending' word.”h]”hŒ%clear the â€˜list_op_pendingâ€™ word.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K’hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjÅ  ubeh}”(h]”h ]”h"]”h$]”h&]”j‚  jƒ  j„  hj…  j†  uh1jE  hjÁ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j?  h³hÊh´Khh·h²hubhì)”}”(hŒOn removal:”h]”hŒOn removal:”…””}”(hj3  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K”hh·h²hubj@  )”}”(hŒØ1) set the 'list_op_pending' word to the address of the 'lock entry'
   to be removed,
2) remove the lock entry for this lock from the 'head' list,
3) release the futex lock, and
4) clear the 'lock_op_pending' word.
”h]”jF  )”}”(hhh]”(jK  )”}”(hŒPset the 'list_op_pending' word to the address of the 'lock entry'
to be removed,”h]”hì)”}”(hŒPset the 'list_op_pending' word to the address of the 'lock entry'
to be removed,”h]”hŒXset the â€˜list_op_pendingâ€™ word to the address of the â€˜lock entryâ€™
to be removed,”…””}”(hjL  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K–hjH  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjE  ubjK  )”}”(hŒ9remove the lock entry for this lock from the 'head' list,”h]”hì)”}”(hjb  h]”hŒ=remove the lock entry for this lock from the â€˜headâ€™ list,”…””}”(hjd  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K˜hj`  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjE  ubjK  )”}”(hŒrelease the futex lock, and”h]”hì)”}”(hjy  h]”hŒrelease the futex lock, and”…””}”(hj{  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K™hjw  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjE  ubjK  )”}”(hŒ"clear the 'lock_op_pending' word.
”h]”hì)”}”(hŒ!clear the 'lock_op_pending' word.”h]”hŒ%clear the â€˜lock_op_pendingâ€™ word.”…””}”(hj’  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´KšhjŽ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjE  ubeh}”(h]”h ]”h"]”h$]”h&]”j‚  jƒ  j„  hj…  j†  uh1jE  hjA  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j?  h³hÊh´K–hh·h²hubhì)”}”(hXE  On exit, the kernel will consider the address stored in
'list_op_pending' and the address of each 'lock word' found by walking
the list starting at 'head'.  For each such address, if the bottom 30
bits of the 'lock word' at offset 'offset' from that address equals the
exiting threads TID, then the kernel will do two things:”h]”hXY  On exit, the kernel will consider the address stored in
â€˜list_op_pendingâ€™ and the address of each â€˜lock wordâ€™ found by walking
the list starting at â€˜headâ€™.  For each such address, if the bottom 30
bits of the â€˜lock wordâ€™ at offset â€˜offsetâ€™ from that address equals the
exiting threads TID, then the kernel will do two things:”…””}”(hj²  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´Kœhh·h²hubj@  )”}”(hX   1) if bit 31 (0x80000000) is set in that word, then attempt a futex
   wakeup on that address, which will waken the next thread that has
   used to the futex mechanism to wait on that address, and
2) atomically set  bit 30 (0x40000000) in the 'lock word'.
”h]”jF  )”}”(hhh]”(jK  )”}”(hŒ»if bit 31 (0x80000000) is set in that word, then attempt a futex
wakeup on that address, which will waken the next thread that has
used to the futex mechanism to wait on that address, and”h]”hì)”}”(hŒ»if bit 31 (0x80000000) is set in that word, then attempt a futex
wakeup on that address, which will waken the next thread that has
used to the futex mechanism to wait on that address, and”h]”hŒ»if bit 31 (0x80000000) is set in that word, then attempt a futex
wakeup on that address, which will waken the next thread that has
used to the futex mechanism to wait on that address, and”…””}”(hjË  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K¢hjÇ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjÄ  ubjK  )”}”(hŒ8atomically set  bit 30 (0x40000000) in the 'lock word'.
”h]”hì)”}”(hŒ7atomically set  bit 30 (0x40000000) in the 'lock word'.”h]”hŒ;atomically set  bit 30 (0x40000000) in the â€˜lock wordâ€™.”…””}”(hjã  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K¥hjß  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hjÄ  ubeh}”(h]”h ]”h"]”h$]”h&]”j‚  jƒ  j„  hj…  j†  uh1jE  hjÀ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j?  h³hÊh´K¢hh·h²hubhì)”}”(hŒ°In the above, bit 31 was set by futex waiters on that lock to indicate
they were waiting, and bit 30 is set by the kernel to indicate that the
lock owner died holding the lock.”h]”hŒ°In the above, bit 31 was set by futex waiters on that lock to indicate
they were waiting, and bit 30 is set by the kernel to indicate that the
lock owner died holding the lock.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K§hh·h²hubhì)”}”(hŒRThe kernel exit code will silently stop scanning the list further if at
any point:”h]”hŒRThe kernel exit code will silently stop scanning the list further if at
any point:”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K«hh·h²hubj@  )”}”(hXU  1) the 'head' pointer or an subsequent linked list pointer
   is not a valid address of a user space word
2) the calculated location of the 'lock word' (address plus
   'offset') is not the valid address of a 32 bit user space
   word
3) if the list contains more than 1 million (subject to
   future kernel configuration changes) elements.
”h]”jF  )”}”(hhh]”(jK  )”}”(hŒcthe 'head' pointer or an subsequent linked list pointer
is not a valid address of a user space word”h]”hì)”}”(hŒcthe 'head' pointer or an subsequent linked list pointer
is not a valid address of a user space word”h]”hŒgthe â€˜headâ€™ pointer or an subsequent linked list pointer
is not a valid address of a user space word”…””}”(hj*  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K®hj&  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hj#  ubjK  )”}”(hŒwthe calculated location of the 'lock word' (address plus
'offset') is not the valid address of a 32 bit user space
word”h]”hì)”}”(hŒwthe calculated location of the 'lock word' (address plus
'offset') is not the valid address of a 32 bit user space
word”h]”hŒthe calculated location of the â€˜lock wordâ€™ (address plus
â€˜offsetâ€™) is not the valid address of a 32 bit user space
word”…””}”(hjB  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K°hj>  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hj#  ubjK  )”}”(hŒdif the list contains more than 1 million (subject to
future kernel configuration changes) elements.
”h]”hì)”}”(hŒcif the list contains more than 1 million (subject to
future kernel configuration changes) elements.”h]”hŒcif the list contains more than 1 million (subject to
future kernel configuration changes) elements.”…””}”(hjZ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hëh³hÊh´K³hjV  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jJ  hj#  ubeh}”(h]”h ]”h"]”h$]”h&]”j‚  jƒ  j„  hj…  j†  uh1jE  hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j?  h³hÊh´K®hh·h²hubhì)”}”(hŒ®When the kernel sees a list entry whose 'lock word' doesn't have the
current threads TID in the lower 30 bits, it does nothing with that
entry, and goes on to the next entry.”h]”hŒ´When the kernel sees a list entry whose â€˜lock wordâ€™ doesnâ€™t have the
current threads TID in the lower 30 bits, it does nothing with that
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decoration”Nh²hub.