On Tue, Mar 01, 2016 at 01:44:32PM -0800, Dan Williams wrote:
> Given we have uninitialized list_heads being passed to list_add() it
> will always be the case that those uninitialized values randomly trigger
> the poison value. Especially since a list_add() operation will seed the
> stack with the poison value for later stack allocations to trip over.
> For example, see these two false positive reports:
>
> list_add attempted on force-poisoned entry
> WARNING: at lib/list_debug.c:34
> [..]
> NIP [c00000000043c390] __list_add+0xb0/0x150
> LR [c00000000043c38c] __list_add+0xac/0x150
> Call Trace:
> [c000000fb5fc3320] [c00000000043c38c] __list_add+0xac/0x150 (unreliable)
> [c000000fb5fc33a0] [c00000000081b454] __down+0x4c/0xf8
> [c000000fb5fc3410] [c00000000010b6f8] down+0x68/0x70
> [c000000fb5fc3450] [d0000000201ebf4c] xfs_buf_lock+0x4c/0x150 [xfs]
>
> list_add attempted on force-poisoned entry(0000000000000500),
> new->next == d0000000059ecdb0, new->prev == 0000000000000500
> WARNING: at lib/list_debug.c:33
> [..]
> NIP [c00000000042db78] __list_add+0xa8/0x140
> LR [c00000000042db74] __list_add+0xa4/0x140
> Call Trace:
> [c0000004c749f620] [c00000000042db74] __list_add+0xa4/0x140 (unreliable)
> [c0000004c749f6b0] [c0000000008010ec] rwsem_down_read_failed+0x6c/0x1a0
> [c0000004c749f760] [c000000000800828] down_read+0x58/0x60
> [c0000004c749f7e0] [d000000005a1a6bc] xfs_log_commit_cil+0x7c/0x600 [xfs]
>
> Reported-by: Eryu Guan <eguan@xxxxxxxxxx>
> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Cc: <xfs@xxxxxxxxxxx>
> Fixes: commit 5c2c2587b132 ("mm, dax, pmem: introduce {get|put}_dev_pagemap() for dax-gup")
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
With this patch applied, I don't see the warning after 1000 iterations
(of course, the warning has been removed :-)).
Thanks!
Eryu
P.S.
With the RFC patch posted eariler, warnings are still triggered.
> ---
> include/linux/list.h | 11 -----------
> kernel/memremap.c | 9 +++++++--
> lib/list_debug.c | 9 ---------
> 3 files changed, 7 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/list.h b/include/linux/list.h
> index 30cf4200ab40..5356f4d661a7 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -113,17 +113,6 @@ extern void __list_del_entry(struct list_head *entry);
> extern void list_del(struct list_head *entry);
> #endif
>
> -#ifdef CONFIG_DEBUG_LIST
> -/*
> - * See devm_memremap_pages() which wants DEBUG_LIST=y to assert if one
> - * of the pages it allocates is ever passed to list_add()
> - */
> -extern void list_force_poison(struct list_head *entry);
> -#else
> -/* fallback to the less strict LIST_POISON* definitions */
> -#define list_force_poison list_del
> -#endif
> -
> /**
> * list_replace - replace old entry by new one
> * @old : the element to be replaced
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index b981a7b023f0..778191e3e887 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -351,8 +351,13 @@ void *devm_memremap_pages(struct device *dev, struct resource *res,
> for_each_device_pfn(pfn, page_map) {
> struct page *page = pfn_to_page(pfn);
>
> - /* ZONE_DEVICE pages must never appear on a slab lru */
> - list_force_poison(&page->lru);
> + /*
> + * ZONE_DEVICE pages union ->lru with a ->pgmap back
> + * pointer. It is a bug if a ZONE_DEVICE page is ever
> + * freed or placed on a driver-private list. Seed the
> + * storage with LIST_POISON* values.
> + */
> + list_del(&page->lru);
> page->pgmap = pgmap;
> }
> devres_add(dev, page_map);
> diff --git a/lib/list_debug.c b/lib/list_debug.c
> index 3345a089ef7b..3859bf63561c 100644
> --- a/lib/list_debug.c
> +++ b/lib/list_debug.c
> @@ -12,13 +12,6 @@
> #include <linux/kernel.h>
> #include <linux/rculist.h>
>
> -static struct list_head force_poison;
> -void list_force_poison(struct list_head *entry)
> -{
> - entry->next = &force_poison;
> - entry->prev = &force_poison;
> -}
> -
> /*
> * Insert a new entry between two known consecutive entries.
> *
> @@ -30,8 +23,6 @@ void __list_add(struct list_head *new,
> struct list_head *prev,
> struct list_head *next)
> {
> - WARN(new->next == &force_poison || new->prev == &force_poison,
> - "list_add attempted on force-poisoned entry\n");
> WARN(next->prev != prev,
> "list_add corruption. next->prev should be "
> "prev (%p), but was %p. (next=%p).\n",
>
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