From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hiroshi Shimamoto Subject: [PATCH -rt] avoid deadlock related with PG_nonewrefs and swap_lock Date: Mon, 24 Mar 2008 11:24:17 -0700 Message-ID: <47E7F1D1.6010407@ct.jp.nec.com> References: <47DEB7F0.8040207@ct.jp.nec.com> <47DF097B.4090200@ct.jp.nec.com> <1205833218.8514.338.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Steven Rostedt , linux-rt-users , Ingo Molnar , Thomas Gleixner , LKML To: Peter Zijlstra Return-path: In-Reply-To: <1205833218.8514.338.camel@twins> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org Hi Peter, I've updated the patch. Could you please review it? I'm also thinking that it can be in the mainline because it makes the lock period shorter, correct? --- From: Hiroshi Shimamoto There is a deadlock scenario; remove_mapping() vs free_swap_and_cache(). remove_mapping() turns PG_nonewrefs bit on, then locks swap_lock. free_swap_and_cache() locks swap_lock, then wait to turn PG_nonewrefs bit off in find_get_page(). swap_lock can be unlocked before calling find_get_page(). In remove_exclusive_swap_page(), there is similar lock sequence; swap_lock, then PG_nonewrefs bit. swap_lock can be unlocked before turning PG_nonewrefs bit on. Signed-off-by: Hiroshi Shimamoto --- mm/swapfile.c | 10 ++++++---- 1 files changed, 6 insertions(+), 4 deletions(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index 5036b70..6fbc77e 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -366,6 +366,7 @@ int remove_exclusive_swap_page(struct page *page) /* Is the only swap cache user the cache itself? */ retval = 0; if (p->swap_map[swp_offset(entry)] == 1) { + spin_unlock(&swap_lock); /* Recheck the page count with the swapcache lock held.. */ lock_page_ref_irq(page); if ((page_count(page) == 2) && !PageWriteback(page)) { @@ -374,8 +375,8 @@ int remove_exclusive_swap_page(struct page *page) retval = 1; } unlock_page_ref_irq(page); - } - spin_unlock(&swap_lock); + } else + spin_unlock(&swap_lock); if (retval) { swap_free(entry); @@ -400,13 +401,14 @@ void free_swap_and_cache(swp_entry_t entry) p = swap_info_get(entry); if (p) { if (swap_entry_free(p, swp_offset(entry)) == 1) { + spin_unlock(&swap_lock); page = find_get_page(&swapper_space, entry.val); if (page && unlikely(TestSetPageLocked(page))) { page_cache_release(page); page = NULL; } - } - spin_unlock(&swap_lock); + } else + spin_unlock(&swap_lock); } if (page) { int one_user; -- 1.5.4.1