Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753765Ab3JLCuF (ORCPT ); Fri, 11 Oct 2013 22:50:05 -0400 Received: from mail-vb0-f41.google.com ([209.85.212.41]:56808 "EHLO mail-vb0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751680Ab3JLCuD (ORCPT ); Fri, 11 Oct 2013 22:50:03 -0400 MIME-Version: 1.0 In-Reply-To: <20131011071259.GC6847@bbox> References: <000201ceb836$4c549740$e4fdc5c0$%yang@samsung.com> <20130924010308.GG17725@bbox> <000001ceba6a$997d0490$cc770db0$%yang@samsung.com> <20131011071259.GC6847@bbox> Date: Sat, 12 Oct 2013 10:50:01 +0800 Message-ID: Subject: Re: [PATCH v3 2/3] mm/zswap: bugfix: memory leak when invalidate and reclaim occur concurrently From: Bob Liu To: Minchan Kim Cc: Weijie Yang , Andrew Morton , Seth Jennings , Bob Liu , Weijie Yang , Linux-MM , Linux-Kernel , stable@vger.kernel.org, d.j.shin@samsung.com, heesub.shin@samsung.com, Kyungmin Park , hau.chen@samsung.com, bifeng.tong@samsung.com, rui.xie@samsung.com Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9197 Lines: 252 On Fri, Oct 11, 2013 at 3:13 PM, Minchan Kim wrote: > On Thu, Sep 26, 2013 at 11:42:17AM +0800, Weijie Yang wrote: >> On Tue, Sep 24, 2013 at 9:03 AM, Minchan Kim wrote: >> > On Mon, Sep 23, 2013 at 04:21:49PM +0800, Weijie Yang wrote: >> > > >> > > Modify: >> > > - check the refcount in fail path, free memory if it is not referenced. >> > >> > Hmm, I don't like this because zswap refcount routine is already mess for me. >> > I'm not sure why it was designed from the beginning. I hope we should fix it first. >> > >> > 1. zswap_rb_serach could include zswap_entry_get semantic if it founds a entry from >> > the tree. Of course, we should ranme it as find_get_zswap_entry like find_get_page. >> > 2. zswap_entry_put could hide resource free function like zswap_free_entry so that >> > all of caller can use it easily following pattern. >> > >> > find_get_zswap_entry >> > ... >> > ... >> > zswap_entry_put >> > >> > Of course, zswap_entry_put have to check the entry is in the tree or not >> > so if someone already removes it from the tree, it should avoid double remove. >> > >> > One of the concern I can think is that approach extends critical section >> > but I think it would be no problem because more bottleneck would be [de]compress >> > functions. If it were really problem, we can mitigate a problem with moving >> > unnecessary functions out of zswap_free_entry because it seem to be rather >> > over-enginnering. >> >> I refactor the zswap refcount routine according to Minchan's idea. >> Here is the new patch, Any suggestion is welcomed. >> >> To Seth and Bob, would you please review it again? > > Yeah, Seth, Bob. You guys are right persons to review this because this > scheme was suggested by me who is biased so it couldn't be a fair. ;-) > But anyway, I will review code itself. > >> >> mm/zswap.c | 116 >> ++++++++++++++++++++++++++++++++++++++++++++++++++++---------------------------------------------------------------- >> 1 file changed, 52 insertions(+), 64 deletions(-) >> >> diff --git a/mm/zswap.c b/mm/zswap.c >> old mode 100644 >> new mode 100755 >> index deda2b6..bd04910 >> --- a/mm/zswap.c >> +++ b/mm/zswap.c >> @@ -217,6 +217,7 @@ static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) >> if (!entry) >> return NULL; >> entry->refcount = 1; >> + RB_CLEAR_NODE(&entry->rbnode); >> return entry; >> } >> >> @@ -232,10 +233,20 @@ static void zswap_entry_get(struct zswap_entry *entry) >> } >> >> /* caller must hold the tree lock */ >> -static int zswap_entry_put(struct zswap_entry *entry) >> +static int zswap_entry_put(struct zswap_tree *tree, struct zswap_entry *entry) > > Why should we have return value? If we really need it, it mitigates > get/put semantic's whole point so I'd like to just return void. > > Let me see. > >> { >> - entry->refcount--; >> - return entry->refcount; >> + int refcount = --entry->refcount; >> + >> + if (refcount <= 0) { > > Hmm, I don't like minus refcount, really. > I hope we could do following as > > BUG_ON(refcount < 0); > if (refcount == 0) { > ... > } > > > >> + if (!RB_EMPTY_NODE(&entry->rbnode)) { >> + rb_erase(&entry->rbnode, &tree->rbroot); >> + RB_CLEAR_NODE(&entry->rbnode); > > Minor, > You could make new function zswap_rb_del or zswap_rb_remove which detach the node > from rb tree and clear node because we have already zswap_rb_insert. > > >> + } >> + >> + zswap_free_entry(tree, entry); >> + } >> + >> + return refcount; >> } >> >> /********************************* >> @@ -258,6 +269,17 @@ static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset) >> return NULL; >> } >> > > Add function description. > >> +static struct zswap_entry *zswap_entry_find_get(struct rb_root *root, pgoff_t offset) >> +{ >> + struct zswap_entry *entry = NULL; >> + >> + entry = zswap_rb_search(root, offset); >> + if (entry) >> + zswap_entry_get(entry); >> + >> + return entry; >> +} >> + >> /* >> * In the case that a entry with the same offset is found, a pointer to >> * the existing entry is stored in dupentry and the function returns -EEXIST >> @@ -387,7 +409,7 @@ static void zswap_free_entry(struct zswap_tree *tree, struct zswap_entry *entry) >> enum zswap_get_swap_ret { >> ZSWAP_SWAPCACHE_NEW, >> ZSWAP_SWAPCACHE_EXIST, >> - ZSWAP_SWAPCACHE_NOMEM >> + ZSWAP_SWAPCACHE_FAIL, >> }; >> >> /* >> @@ -401,9 +423,9 @@ enum zswap_get_swap_ret { >> * added to the swap cache, and returned in retpage. >> * >> * If success, the swap cache page is returned in retpage >> - * Returns 0 if page was already in the swap cache, page is not locked >> - * Returns 1 if the new page needs to be populated, page is locked >> - * Returns <0 on error >> + * Returns ZSWAP_SWAPCACHE_EXIST if page was already in the swap cache >> + * Returns ZSWAP_SWAPCACHE_NEW if the new page needs to be populated, page is locked >> + * Returns ZSWAP_SWAPCACHE_FAIL on error >> */ >> static int zswap_get_swap_cache_page(swp_entry_t entry, >> struct page **retpage) >> @@ -475,7 +497,7 @@ static int zswap_get_swap_cache_page(swp_entry_t entry, >> if (new_page) >> page_cache_release(new_page); >> if (!found_page) >> - return ZSWAP_SWAPCACHE_NOMEM; >> + return ZSWAP_SWAPCACHE_FAIL; >> *retpage = found_page; >> return ZSWAP_SWAPCACHE_EXIST; >> } >> @@ -517,23 +539,22 @@ static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle) >> >> /* find and ref zswap entry */ >> spin_lock(&tree->lock); >> - entry = zswap_rb_search(&tree->rbroot, offset); >> + entry = zswap_entry_find_get(&tree->rbroot, offset); >> if (!entry) { >> /* entry was invalidated */ >> spin_unlock(&tree->lock); >> return 0; >> } >> - zswap_entry_get(entry); >> spin_unlock(&tree->lock); >> BUG_ON(offset != entry->offset); >> >> /* try to allocate swap cache page */ >> switch (zswap_get_swap_cache_page(swpentry, &page)) { >> - case ZSWAP_SWAPCACHE_NOMEM: /* no memory */ >> + case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */ >> ret = -ENOMEM; >> goto fail; >> >> - case ZSWAP_SWAPCACHE_EXIST: /* page is unlocked */ >> + case ZSWAP_SWAPCACHE_EXIST: > > Why did you remove comment? > >> /* page is already in the swap cache, ignore for now */ >> page_cache_release(page); >> ret = -EEXIST; >> @@ -562,38 +583,28 @@ static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle) >> zswap_written_back_pages++; >> >> spin_lock(&tree->lock); >> - >> /* drop local reference */ >> - zswap_entry_put(entry); >> + refcount = zswap_entry_put(tree, entry); >> /* drop the initial reference from entry creation */ >> - refcount = zswap_entry_put(entry); >> - >> - /* >> - * There are three possible values for refcount here: >> - * (1) refcount is 1, load is in progress, unlink from rbtree, >> - * load will free >> - * (2) refcount is 0, (normal case) entry is valid, >> - * remove from rbtree and free entry >> - * (3) refcount is -1, invalidate happened during writeback, >> - * free entry >> - */ >> - if (refcount >= 0) { >> - /* no invalidate yet, remove from rbtree */ >> + if (refcount > 0) { >> rb_erase(&entry->rbnode, &tree->rbroot); >> + RB_CLEAR_NODE(&entry->rbnode); >> + refcount = zswap_entry_put(tree, entry); > > Now, I see why you need return in zswap_entry_put but let's consider again > because it's really mess to me and it hurts get/put semantic a lot so > How about this? > > spin_lock(&tree->lock); > /* drop local reference */ > zswap_entry_put(tree, entry); > /* > * In here, we want to free entry but invalidation may free earlier > * under us so that we should check it again > */ > if (entry == zswap_rb_search(&tree->rb_root, offset)) Then where is the place unlink entry from rbtree if load was in progress ? And in the following fail path, return value from zswap_entry_put() is also used. > /* Yes, it's stable so we should free it */ > zswap_entry_put(tree, entry); > > /* > * Whether it would be freed by invalidation or writeback, it doesn't > * matter. Important thing is that it will be freed so there > * is no point to return -EAGAIN. > */ > spin_unlock(&tree->lock); > return 0; > -- Regards, --Bob -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/