When we upgraded our kernel, we started seeing some page corruption like the following consistently:
BUG: Bad page state in process ganesha.nfsd pfn:1304ca page:0000000022261c55 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x0 pfn:0x1304ca flags: 0x17ffffc0000000() raw: 0017ffffc0000000 ffff8a513ffd4c98 ffffeee24b35ec08 0000000000000000 raw: 0000000000000000 0000000000000001 00000000ffffff7f 0000000000000000 page dumped because: nonzero mapcount CPU: 0 PID: 15567 Comm: ganesha.nfsd Kdump: loaded Tainted: P B O 5.10.158-1.nutanix.20221209.el7.x86_64 #1 Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 04/05/2016 Call Trace: dump_stack+0x74/0x96 bad_page.cold+0x63/0x94 check_new_page_bad+0x6d/0x80 rmqueue+0x46e/0x970 get_page_from_freelist+0xcb/0x3f0 ? _cond_resched+0x19/0x40 __alloc_pages_nodemask+0x164/0x300 alloc_pages_current+0x87/0xf0 skb_page_frag_refill+0x84/0x110 ...
Sometimes, it would also show up as corruption in the free list pointer and cause crashes.
After bisecting the issue, we found the issue started from e320d3012d25:
if (put_page_testzero(page)) free_the_page(page, order); else if (!PageHead(page)) while (order-- > 0) free_the_page(page + (1 << order), order);
So the problem is the check PageHead is racy because at this point we already dropped our reference to the page. So even if we came in with compound page, the page can already be freed and PageHead can return false and we will end up freeing all the tail pages causing double free.
Fixes: e320d3012d25 ("mm/page_alloc.c: fix freeing non-compound pages") Cc: Andrew Morton akpm@linux-foundation.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: linux-mm@kvack.org Cc: stable@vger.kernel.org Signed-off-by: Chunwei Chen david.chen@nutanix.com --- mm/page_alloc.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 0745aedebb37..3bb3484563ed 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5631,9 +5631,12 @@ EXPORT_SYMBOL(get_zeroed_page); */ void __free_pages(struct page *page, unsigned int order) { + /* get PageHead before we drop reference */ + int head = PageHead(page); + if (put_page_testzero(page)) free_the_page(page, order); - else if (!PageHead(page)) + else if (!head) while (order-- > 0) free_the_page(page + (1 << order), order); }
On Thu, Feb 09, 2023 at 05:48:28PM +0000, David Chen wrote:
So the problem is the check PageHead is racy because at this point we already dropped our reference to the page. So even if we came in with compound page, the page can already be freed and PageHead can return false and we will end up freeing all the tail pages causing double free.
Fixes: e320d3012d25 ("mm/page_alloc.c: fix freeing non-compound pages") Cc: Andrew Morton akpm@linux-foundation.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: linux-mm@kvack.org Cc: stable@vger.kernel.org Signed-off-by: Chunwei Chen david.chen@nutanix.com
Reviewed-by: Matthew Wilcox (Oracle) willy@infradead.org
That's a pretty narrow window you managed to hit! Just a few instructions wide. I guess that answers the question Andrew originally had (Does this ever happen?) I just changed it from a silent memory leak into a double-free.
mm/page_alloc.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 0745aedebb37..3bb3484563ed 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5631,9 +5631,12 @@ EXPORT_SYMBOL(get_zeroed_page); */ void __free_pages(struct page *page, unsigned int order) {
- /* get PageHead before we drop reference */
- int head = PageHead(page);
- if (put_page_testzero(page)) free_the_page(page, order);
- else if (!PageHead(page))
- else if (!head) while (order-- > 0) free_the_page(page + (1 << order), order);
}
2.22.3
On 2/9/23 18:48, David Chen wrote:
When we upgraded our kernel, we started seeing some page corruption like the following consistently:
BUG: Bad page state in process ganesha.nfsd pfn:1304ca page:0000000022261c55 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x0 pfn:0x1304ca flags: 0x17ffffc0000000() raw: 0017ffffc0000000 ffff8a513ffd4c98 ffffeee24b35ec08 0000000000000000 raw: 0000000000000000 0000000000000001 00000000ffffff7f 0000000000000000 page dumped because: nonzero mapcount CPU: 0 PID: 15567 Comm: ganesha.nfsd Kdump: loaded Tainted: P B O 5.10.158-1.nutanix.20221209.el7.x86_64 #1 Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 04/05/2016 Call Trace: dump_stack+0x74/0x96 bad_page.cold+0x63/0x94 check_new_page_bad+0x6d/0x80 rmqueue+0x46e/0x970 get_page_from_freelist+0xcb/0x3f0 ? _cond_resched+0x19/0x40 __alloc_pages_nodemask+0x164/0x300 alloc_pages_current+0x87/0xf0 skb_page_frag_refill+0x84/0x110 ...
Sometimes, it would also show up as corruption in the free list pointer and cause crashes.
After bisecting the issue, we found the issue started from e320d3012d25:
if (put_page_testzero(page)) free_the_page(page, order); else if (!PageHead(page)) while (order-- > 0) free_the_page(page + (1 << order), order);
So the problem is the check PageHead is racy because at this point we already dropped our reference to the page. So even if we came in with compound page, the page can already be freed and PageHead can return false and we will end up freeing all the tail pages causing double free.
Fixes: e320d3012d25 ("mm/page_alloc.c: fix freeing non-compound pages") Cc: Andrew Morton akpm@linux-foundation.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: linux-mm@kvack.org Cc: stable@vger.kernel.org Signed-off-by: Chunwei Chen david.chen@nutanix.com
Reviewed-by: Vlastimil Babka vbabka@suse.cz
That's nasty enough to go into 6.2, IMHO.
mm/page_alloc.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 0745aedebb37..3bb3484563ed 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5631,9 +5631,12 @@ EXPORT_SYMBOL(get_zeroed_page); */ void __free_pages(struct page *page, unsigned int order) {
- /* get PageHead before we drop reference */
- int head = PageHead(page);
- if (put_page_testzero(page)) free_the_page(page, order);
- else if (!PageHead(page))
- else if (!head) while (order-- > 0) free_the_page(page + (1 << order), order);
}
[TLDR: I'm adding this report to the list of tracked Linux kernel regressions; the text you find below is based on a few templates paragraphs you might have encountered already in similar form. See link in footer if these mails annoy you.]
On 09.02.23 18:48, David Chen wrote:
When we upgraded our kernel, we started seeing some page corruption like the following consistently:
BUG: Bad page state in process ganesha.nfsd pfn:1304ca page:0000000022261c55 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x0 pfn:0x1304ca flags: 0x17ffffc0000000() raw: 0017ffffc0000000 ffff8a513ffd4c98 ffffeee24b35ec08 0000000000000000 raw: 0000000000000000 0000000000000001 00000000ffffff7f 0000000000000000 page dumped because: nonzero mapcount CPU: 0 PID: 15567 Comm: ganesha.nfsd Kdump: loaded Tainted: P B O 5.10.158-1.nutanix.20221209.el7.x86_64 #1 Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 04/05/2016 Call Trace: dump_stack+0x74/0x96 bad_page.cold+0x63/0x94 check_new_page_bad+0x6d/0x80 rmqueue+0x46e/0x970 get_page_from_freelist+0xcb/0x3f0 ? _cond_resched+0x19/0x40 __alloc_pages_nodemask+0x164/0x300 alloc_pages_current+0x87/0xf0 skb_page_frag_refill+0x84/0x110 ...
Sometimes, it would also show up as corruption in the free list pointer and cause crashes.
After bisecting the issue, we found the issue started from e320d3012d25:
if (put_page_testzero(page)) free_the_page(page, order); else if (!PageHead(page)) while (order-- > 0) free_the_page(page + (1 << order), order);
So the problem is the check PageHead is racy because at this point we already dropped our reference to the page. So even if we came in with compound page, the page can already be freed and PageHead can return false and we will end up freeing all the tail pages causing double free.
Fixes: e320d3012d25 ("mm/page_alloc.c: fix freeing non-compound pages") Cc: Andrew Morton akpm@linux-foundation.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: linux-mm@kvack.org Cc: stable@vger.kernel.org Signed-off-by: Chunwei Chen david.chen@nutanix.com
Thanks for the report and the patch. To be sure the issue doesn't fall through the cracks unnoticed, I'm adding it to regzbot, the Linux kernel regression tracking bot:
#regzbot ^introduced e320d3012d25 #regzbot title mm: page corruption caused by racy check in __free_pages #regzbot ignore-activity
Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat) -- Everything you wanna know about Linux kernel regression tracking: https://linux-regtracking.leemhuis.info/about/#tldr That page also explains what to do if mails like this annoy you.
linux-stable-mirror@lists.linaro.org
-
David Chen -
Linux regression tracking #adding (Thorsten Leemhuis) -
Matthew Wilcox -
Vlastimil Babka