mm: refactor reinsert of swap_info in sys_swapoff() (cf0cac0a) · Commits · 戴 / test

The block within sys_swapoff() which re-inserts the swap_info into the swap_list in case of failure of try_to_unuse() reads a few values outside the swap_lock. While this is safe at that point, it is subtle code. Simplify the code by moving the reading of these values to a separate function, refactoring it a bit so they are read from within the swap_lock. This is easier to understand, and matches better the way it worked before I unified the insertion of the swap_info from both sys_swapon and sys_swapoff. This change should make no functional difference. The only real change is moving the read of two or three structure fields to within the lock (frontswap_map_get() is nothing more than a read of p->frontswap_map). Signed-off-by:

Cesar Eduardo Barros <cesarb@cesarb.net> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Dan Magenheimer <dan.magenheimer@oracle.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Hugh Dickins <hughd@google.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/swapfile.c

+17 −9

Original line number	Diff line number	Diff line
		@@ -1443,13 +1443,12 @@ static int setup_swap_extents(struct swap_info_struct sis, sector_t span)
		return generic_swapfile_activate(sis, swap_file, span);
		}

		static void enable_swap_info(struct swap_info_struct *p, int prio,
		static void _enable_swap_info(struct swap_info_struct *p, int prio,
		unsigned char *swap_map,
		unsigned long *frontswap_map)
		{
		int i, prev;

		spin_lock(&swap_lock);
		if (prio >= 0)
		p->prio = prio;
		else
		@@ -1473,6 +1472,21 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
		else
		swap_info[prev]->next = p->type;
		frontswap_init(p->type);
		}

		static void enable_swap_info(struct swap_info_struct *p, int prio,
		unsigned char *swap_map,
		unsigned long *frontswap_map)
		{
		spin_lock(&swap_lock);
		_enable_swap_info(p, prio, swap_map, frontswap_map);
		spin_unlock(&swap_lock);
		}

		static void reinsert_swap_info(struct swap_info_struct *p)
		{
		spin_lock(&swap_lock);
		_enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
		spin_unlock(&swap_lock);
		}

		@@ -1548,14 +1562,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
		compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX, oom_score_adj);

		if (err) {
		/*
		* reading p->prio and p->swap_map outside the lock is
		* safe here because only sys_swapon and sys_swapoff
		* change them, and there can be no other sys_swapon or
		* sys_swapoff for this swap_info_struct at this point.
		*/
		/* re-insert swap space back into swap_list */
		enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
		reinsert_swap_info(p);
		goto out_dput;
		}

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