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a5c9b696ec
If a kthread happens to use get_user_pages() on an mm (as KSM does), there's a chance that it will end up trying to read in a swap page, then oops in grab_swap_token() because the kthread has no mm: GUP passes down the right mm, so grab_swap_token() ought to be using it. We have not identified a stronger case than KSM's daemon (not yet in mainline), but the issue must have come up before, since RHEL has included a fix for this for years (though a different fix, they just back out of grab_swap_token if current->mm is unset: which is what we first proposed, but using the right mm here seems more correct). Reported-by: Izik Eidus <ieidus@redhat.com> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
78 lines
1.9 KiB
C
78 lines
1.9 KiB
C
/*
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* mm/thrash.c
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*
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* Copyright (C) 2004, Red Hat, Inc.
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* Copyright (C) 2004, Rik van Riel <riel@redhat.com>
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* Released under the GPL, see the file COPYING for details.
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*
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* Simple token based thrashing protection, using the algorithm
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* described in: http://www.cs.wm.edu/~sjiang/token.pdf
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*
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* Sep 2006, Ashwin Chaugule <ashwin.chaugule@celunite.com>
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* Improved algorithm to pass token:
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* Each task has a priority which is incremented if it contended
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* for the token in an interval less than its previous attempt.
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* If the token is acquired, that task's priority is boosted to prevent
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* the token from bouncing around too often and to let the task make
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* some progress in its execution.
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*/
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#include <linux/jiffies.h>
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#include <linux/mm.h>
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#include <linux/sched.h>
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#include <linux/swap.h>
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static DEFINE_SPINLOCK(swap_token_lock);
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struct mm_struct *swap_token_mm;
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static unsigned int global_faults;
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void grab_swap_token(struct mm_struct *mm)
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{
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int current_interval;
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global_faults++;
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current_interval = global_faults - mm->faultstamp;
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if (!spin_trylock(&swap_token_lock))
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return;
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/* First come first served */
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if (swap_token_mm == NULL) {
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mm->token_priority = mm->token_priority + 2;
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swap_token_mm = mm;
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goto out;
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}
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if (mm != swap_token_mm) {
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if (current_interval < mm->last_interval)
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mm->token_priority++;
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else {
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if (likely(mm->token_priority > 0))
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mm->token_priority--;
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}
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/* Check if we deserve the token */
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if (mm->token_priority > swap_token_mm->token_priority) {
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mm->token_priority += 2;
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swap_token_mm = mm;
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}
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} else {
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/* Token holder came in again! */
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mm->token_priority += 2;
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}
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out:
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mm->faultstamp = global_faults;
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mm->last_interval = current_interval;
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spin_unlock(&swap_token_lock);
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}
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/* Called on process exit. */
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void __put_swap_token(struct mm_struct *mm)
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{
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spin_lock(&swap_token_lock);
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if (likely(mm == swap_token_mm))
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swap_token_mm = NULL;
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spin_unlock(&swap_token_lock);
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}
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