linux-toradex.git/include/linux/task_work.h, branch v4.13-rc4

task_work: task_work_add() should not succeed after exit_task_work()

2012-09-13T14:47:34+00:00

ed3e694d "move exit_task_work() past exit_files() et.al" destroyed
the add/exit synchronization we had, the caller itself should ensure
task_work_add() can't race with the exiting task.

However, this is not convenient/simple, and the only user which tries
to do this is buggy (see the next patch). Unless the task is current,
there is simply no way to do this in general.

Change exit_task_work()->task_work_run() to use the dummy "work_exited"
entry to let task_work_add() know it should fail.

Signed-off-by: Oleg Nesterov 
Signed-off-by: Peter Zijlstra 
Cc: Al Viro 
Cc: Linus Torvalds 
Cc: Andrew Morton 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/20120826191211.GA4228@redhat.com
Signed-off-by: Ingo Molnar

merge task_work and rcu_head, get rid of separate allocation for keyring case

2012-07-22T19:57:56+00:00

task_work and rcu_head are identical now; merge them (calling the result
struct callback_head, rcu_head #define'd to it), kill separate allocation
in security/keys since we can just use cred->rcu now.

Signed-off-by: Al Viro

trim task_work: get rid of hlist

2012-07-22T19:57:55+00:00

layout based on Oleg's suggestion; single-linked list,
task->task_works points to the last element, forward pointer
from said last element points to head.  I'd still prefer
much more regular scheme with two pointers in task_work,
but...

Signed-off-by: Al Viro

trimming task_work: kill ->data

2012-07-22T19:57:54+00:00

get rid of the only user of ->data; this is _not_ the final variant - in the
end we'll have task_work and rcu_head identical and just use cred->rcu,
at which point the separate allocation will be gone completely.

Signed-off-by: Al Viro

task_work_add: generic process-context callbacks

2012-05-24T02:09:21+00:00

Provide a simple mechanism that allows running code in the (nonatomic)
context of the arbitrary task.

The caller does task_work_add(task, task_work) and this task executes
task_work->func() either from do_notify_resume() or from do_exit().  The
callback can rely on PF_EXITING to detect the latter case.

"struct task_work" can be embedded in another struct, still it has "void
*data" to handle the most common/simple case.

This allows us to kill the ->replacement_session_keyring hack, and
potentially this can have more users.

Performance-wise, this adds 2 "unlikely(!hlist_empty())" checks into
tracehook_notify_resume() and do_exit().  But at the same time we can
remove the "replacement_session_keyring != NULL" checks from
arch/*/signal.c and exit_creds().

Note: task_work_add/task_work_run abuses ->pi_lock.  This is only because
this lock is already used by lookup_pi_state() to synchronize with
do_exit() setting PF_EXITING.  Fortunately the scope of this lock in
task_work.c is really tiny, and the code is unlikely anyway.

Signed-off-by: Oleg Nesterov 
Acked-by: David Howells 
Cc: Thomas Gleixner 
Cc: Richard Kuo 
Cc: Linus Torvalds 
Cc: Alexander Gordeev 
Cc: Chris Zankel 
Cc: David Smith 
Cc: "Frank Ch. Eigler" 
Cc: Geert Uytterhoeven 
Cc: Larry Woodman 
Cc: Peter Zijlstra 
Cc: Tejun Heo 
Cc: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Al Viro