On Monday 23 April 2012 03:09:01 Anton Vorontsov wrote: > 1. 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. > 2. 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
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