On Fri, Jan 08, 2016 at 02:56:14PM -0500, Rafael Aquini wrote: > On Fri, Jan 01, 2016 at 11:36:13AM +0200, Michael S. Tsirkin wrote: > > On Mon, Dec 28, 2015 at 08:35:13AM +0900, Minchan Kim wrote: > > > In balloon_page_dequeue, pages_lock should cover the loop > > > (ie, list_for_each_entry_safe). Otherwise, the cursor page could > > > be isolated by compaction and then list_del by isolation could > > > poison the page->lru.{prev,next} so the loop finally could > > > access wrong address like this. This patch fixes the bug. > > > > > > general protection fault: 0000 [#1] SMP > > > Dumping ftrace buffer: > > > (ftrace buffer empty) > > > Modules linked in: > > > CPU: 2 PID: 82 Comm: vballoon Not tainted 4.4.0-rc5-mm1-access_bit+ #1906 > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > > > task: ffff8800a7ff0000 ti: ffff8800a7fec000 task.ti: ffff8800a7fec000 > > > RIP: 0010:[<ffffffff8115e754>] [<ffffffff8115e754>] balloon_page_dequeue+0x54/0x130 > > > RSP: 0018:ffff8800a7fefdc0 EFLAGS: 00010246 > > > RAX: ffff88013fff9a70 RBX: ffffea000056fe00 RCX: 0000000000002b7d > > > RDX: ffff88013fff9a70 RSI: ffffea000056fe00 RDI: ffff88013fff9a68 > > > RBP: ffff8800a7fefde8 R08: ffffea000056fda0 R09: 0000000000000000 > > > R10: ffff8800a7fefd90 R11: 0000000000000001 R12: dead0000000000e0 > > > R13: ffffea000056fe20 R14: ffff880138809070 R15: ffff880138809060 > > > FS: 0000000000000000(0000) GS:ffff88013fc40000(0000) knlGS:0000000000000000 > > > CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > > > CR2: 00007f229c10e000 CR3: 00000000b8b53000 CR4: 00000000000006a0 > > > Stack: > > > 0000000000000100 ffff880138809088 ffff880138809000 ffff880138809060 > > > 0000000000000046 ffff8800a7fefe28 ffffffff812c86d3 ffff880138809020 > > > ffff880138809000 fffffffffff91900 0000000000000100 ffff880138809060 > > > Call Trace: > > > [<ffffffff812c86d3>] leak_balloon+0x93/0x1a0 > > > [<ffffffff812c8bc7>] balloon+0x217/0x2a0 > > > [<ffffffff8143739e>] ? __schedule+0x31e/0x8b0 > > > [<ffffffff81078160>] ? abort_exclusive_wait+0xb0/0xb0 > > > [<ffffffff812c89b0>] ? update_balloon_stats+0xf0/0xf0 > > > [<ffffffff8105b6e9>] kthread+0xc9/0xe0 > > > [<ffffffff8105b620>] ? kthread_park+0x60/0x60 > > > [<ffffffff8143b4af>] ret_from_fork+0x3f/0x70 > > > [<ffffffff8105b620>] ? kthread_park+0x60/0x60 > > > Code: 8d 60 e0 0f 84 af 00 00 00 48 8b 43 20 a8 01 75 3b 48 89 d8 f0 0f ba 28 00 72 10 48 8b 03 f6 c4 08 75 2f 48 89 df e8 8c 83 f9 ff <49> 8b 44 24 20 4d 8d 6c 24 20 48 83 e8 20 4d 39 f5 74 7a 4c 89 > > > RIP [<ffffffff8115e754>] balloon_page_dequeue+0x54/0x130 > > > RSP <ffff8800a7fefdc0> > > > ---[ end trace 43cf28060d708d5f ]--- > > > Kernel panic - not syncing: Fatal exception > > > Dumping ftrace buffer: > > > (ftrace buffer empty) > > > Kernel Offset: disabled > > > > > > Cc: <stable@xxxxxxxxxxxxxxx> > > > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > > > --- > > > mm/balloon_compaction.c | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c > > > index d3116be5a00f..300117f1a08f 100644 > > > --- a/mm/balloon_compaction.c > > > +++ b/mm/balloon_compaction.c > > > @@ -61,6 +61,7 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info) > > > bool dequeued_page; > > > > > > dequeued_page = false; > > > + spin_lock_irqsave(&b_dev_info->pages_lock, flags); > > > list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) { > > > /* > > > * Block others from accessing the 'page' while we get around > > > @@ -75,15 +76,14 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info) > > > continue; > > > } > > > #endif > > > - spin_lock_irqsave(&b_dev_info->pages_lock, flags); > > > balloon_page_delete(page); > > > __count_vm_event(BALLOON_DEFLATE); > > > - spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); > > > unlock_page(page); > > > dequeued_page = true; > > > break; > > > } > > > } > > > + spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); > > > > > > if (!dequeued_page) { > > > /* > > > > I think this will cause deadlocks. > > > > pages_lock now nests within page lock, balloon_page_putback > > nests them in the reverse order. > > > > Did you test this with lockdep? You really should for > > locking changes, and I'd expect it to warn about this. > > > > Also, there's another issue there I think: after isolation page could > > also get freed before we try to lock it. > > > > We really must take a page reference before touching > > the page. > > > > I think we need something like the below to fix this issue. > > Could you please try this out, and send Tested-by? > > I will repost as a proper patch if this works for you. > > > > Nice catch! Thanks for spotting it. I just have one minor nit. See > below > > > > > diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c > > index d3116be..66d69c5 100644 > > --- a/mm/balloon_compaction.c > > +++ b/mm/balloon_compaction.c > > @@ -56,12 +56,34 @@ EXPORT_SYMBOL_GPL(balloon_page_enqueue); > > */ > > struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info) > > { > > - struct page *page, *tmp; > > + struct page *page; > > unsigned long flags; > > bool dequeued_page; > > + LIST_HEAD(processed); /* protected by b_dev_info->pages_lock */ > > > > dequeued_page = false; > > - list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) { > > + /* > > + * We need to go over b_dev_info->pages and lock each page, > > + * but b_dev_info->pages_lock must nest within page lock. > > + * > > + * To make this safe, remove each page from b_dev_info->pages list > > + * under b_dev_info->pages_lock, then drop this lock. Once list is > > + * empty, re-add them also under b_dev_info->pages_lock. > > + */ > > + spin_lock_irqsave(&b_dev_info->pages_lock, flags); > > + while (!list_empty(&b_dev_info->pages)) { > > + page = list_first_entry(&b_dev_info->pages, typeof(*page), lru); > > + /* move to processed list to avoid going over it another time */ > > + list_move(&page->lru, &processed); > > + > > + if (!get_page_unless_zero(page)) > > + continue; > > + /* > > + * pages_lock nests within page lock, > > + * so drop it before trylock_page > > + */ > > + spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); > > + > > /* > > * Block others from accessing the 'page' while we get around > > * establishing additional references and preparing the 'page' > > @@ -72,6 +94,7 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info) > > if (!PagePrivate(page)) { > > /* raced with isolation */ > > unlock_page(page); > > + put_page(page); > > continue; > > } > > #endif > > @@ -80,11 +103,18 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info) > > __count_vm_event(BALLOON_DEFLATE); > > spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); > > unlock_page(page); > > + put_page(page); > > dequeued_page = true; > > break; > ^^^^[1] > > > } > > + put_page(page); > > + spin_lock_irqsave(&b_dev_info->pages_lock, flags); > > } > > > > + /* re-add remaining entries */ > > + list_splice(&processed, &b_dev_info->pages); > > By breaking the loop at its ordinary and expected way-out case [1] > we'll hit list_splice without holding b_dev_info->pages_lock, won't we? Ouch. right. > perhaps by adding the following on top of your patch we can address that pickle > aforementioned: I'd rather just goto outside or return. But maybe Minchan is right and the original patch is ok. I still need to go into this. > Cheers! > Rafael > -- > > diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c > index 66d69c5..74b3e9c 100644 > --- a/mm/balloon_compaction.c > +++ b/mm/balloon_compaction.c > @@ -58,7 +58,7 @@ struct page *balloon_page_dequeue(struct > balloon_dev_info *b_dev_info) > { > struct page *page; > unsigned long flags; > - bool dequeued_page; > + bool dequeued_page, locked; > LIST_HEAD(processed); /* protected by b_dev_info->pages_lock */ > > dequeued_page = false; > @@ -105,13 +105,17 @@ struct page *balloon_page_dequeue(struct > balloon_dev_info *b_dev_info) > unlock_page(page); > put_page(page); > dequeued_page = true; > + locked = false; > break; > } > put_page(page); > spin_lock_irqsave(&b_dev_info->pages_lock, flags); > + locked = true; > } > > /* re-add remaining entries */ > + if (!locked) > + spin_lock_irqsave(&b_dev_info->pages_lock, flags); > list_splice(&processed, &b_dev_info->pages); > spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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