1 Jun
2012
1 Jun
'12
4:36 a.m.
On Monday 23 April 2012 03:09:01 Anton Vorontsov wrote:
- Working with task->mm w/o getting mm or grabing the task lock is dangerous as ->mm might disappear (exit_mm() assigns NULL under task_lock(), so tasklist lock is not enough).
that isn't a problem for this code as it specifically checks if it's in an atomic section. if it is, then task->mm can't go away on us.
We can't use get_task_mm()/mmput() pair as mmput() might sleep, so we have to take the task lock while handle its mm.
if we're not in an atomic section, then sleeping is fine.
- Checking for process->mm is not enough because process' main thread may exit or detach its mm via use_mm(), but other threads may still have a valid mm.
i don't think it matters for this code (per the reasons above).
To catch this we use find_lock_task_mm(), which walks up all threads and returns an appropriate task (with task lock held).
certainly fine for the non-atomic code path. i guess we'll notice in crashes if it causes a problem in atomic code paths as well. -mike