| Message ID | 20200414075622.69822-1-songmuchun@bytedance.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] mm/ksm: Fix NULL pointer dereference when KSM zero page is enabled | expand |
> to crash when we access vma->vm_mm(its offset is 0x40) later in Will another fine-tuning become relevant also for this wording? > following calltrace is captured in kernel 4.19 with KSM zero page Can the mentioned Linux version trigger any special software development concerns? Will any other tags become helpful in such a case? Regards, Markus
On Tue, Apr 14, 2020 at 5:17 PM Markus Elfring <Markus.Elfring@web.de> wrote: > > > to crash when we access vma->vm_mm(its offset is 0x40) later in > > Will another fine-tuning become relevant also for this wording? > Sorry, I don't understand what this means because of my poor English. Could you explain it again. Thanks. > > > following calltrace is captured in kernel 4.19 with KSM zero page > > Can the mentioned Linux version trigger any special software > development concerns? > > Will any other tags become helpful in such a case? How about changing "following calltrace is captured in kernel 4.19 with KSM zero page" to "The following calltrace is captured with the following patch applied: e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with colouring") " ?
>>> to crash when we access vma->vm_mm(its offset is 0x40) later in >> >> Will another fine-tuning become relevant also for this wording? > > Sorry, I don't understand what this means because of my poor English. Our language knowledge can evolve over time. > Could you explain it again. You integrated a few of my suggestions into your message selection. - Thanks. I wonder why you did not like the following small adjustment possibilities so far. to a crash … vm_mm (its … >> Will any other tags become helpful in such a case? > > How about changing > "following calltrace is captured in kernel 4.19 with KSM zero page" > to > "The following calltrace is captured with the following patch applied: > e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with > colouring") > " > ? I find it unlikely that such a wording alternative would be more appropriate while I became just curious for related development consequences around the usage of a longterm kernel version. Would you like to reuse the term “call trace”? Regards, Markus
On Tue, Apr 14, 2020 at 10:17 PM Markus Elfring <Markus.Elfring@web.de> wrote: > > >>> to crash when we access vma->vm_mm(its offset is 0x40) later in > >> > >> Will another fine-tuning become relevant also for this wording? > > > > Sorry, I don't understand what this means because of my poor English. > > Our language knowledge can evolve over time. > > > > Could you explain it again. > > You integrated a few of my suggestions into your message selection. - Thanks. > I wonder why you did not like the following small adjustment possibilities > so far. > > to a crash … vm_mm (its … > Thanks a lot. I will fix it. > > >> Will any other tags become helpful in such a case? > > > > How about changing > > "following calltrace is captured in kernel 4.19 with KSM zero page" > > to > > "The following calltrace is captured with the following patch applied: > > e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with > > colouring") > > " > > ? > > I find it unlikely that such a wording alternative would be more appropriate > while I became just curious for related development consequences around > the usage of a longterm kernel version. > > Would you like to reuse the term “call trace”? > OK, I will reuse the “call trace”. Thanks again. Anyone else have any suggestions? If not, I will post another v4 version to fix the commit message that Markus mentioned.
diff --git a/mm/ksm.c b/mm/ksm.c index a558da9e71770..69b2f85e22d5b 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -2112,8 +2112,11 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) down_read(&mm->mmap_sem); vma = find_mergeable_vma(mm, rmap_item->address); - err = try_to_merge_one_page(vma, page, - ZERO_PAGE(rmap_item->address)); + if (vma) + err = try_to_merge_one_page(vma, page, + ZERO_PAGE(rmap_item->address)); + else + err = -EFAULT; up_read(&mm->mmap_sem); /* * In case of failure, the page was not really empty, so we
The find_mergeable_vma can return NULL. In this case, it leads to crash when we access vma->vm_mm(its offset is 0x40) later in write_protect_page. And this case did happen on our server. The following calltrace is captured in kernel 4.19 with KSM zero page enabled. So add a vma check to fix it. -------------------------------------------------------------------------- BUG: unable to handle kernel NULL pointer dereference at 0000000000000040 PGD 0 P4D 0 Oops: 0000 [#1] SMP NOPTI CPU: 9 PID: 510 Comm: ksmd Kdump: loaded Tainted: G OE 4.19.36.bsk.9-amd64 #4.19.36.bsk.9 Hardware name: FOXCONN R-5111/GROOT, BIOS IC1B111F 08/17/2019 RIP: 0010:try_to_merge_one_page+0xc7/0x760 Code: 24 58 65 48 33 34 25 28 00 00 00 89 e8 0f 85 a3 06 00 00 48 83 c4 60 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 8b 46 08 a8 01 75 b8 <49> 8b 44 24 40 4c 8d 7c 24 20 b9 07 00 00 00 4c 89 e6 4c 89 ff 48 RSP: 0018:ffffadbdd9fffdb0 EFLAGS: 00010246 RAX: ffffda83ffd4be08 RBX: ffffda83ffd4be40 RCX: 0000002c6e800000 RDX: 0000000000000000 RSI: ffffda83ffd4be40 RDI: 0000000000000000 RBP: ffffa11939f02ec0 R08: 0000000094e1a447 R09: 00000000abe76577 R10: 0000000000000962 R11: 0000000000004e6a R12: 0000000000000000 R13: ffffda83b1e06380 R14: ffffa18f31f072c0 R15: ffffda83ffd4be40 FS: 0000000000000000(0000) GS:ffffa0da43b80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000040 CR3: 0000002c77c0a003 CR4: 00000000007626e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: ? follow_page_pte+0x36d/0x5e0 ksm_scan_thread+0x115e/0x1960 ? remove_wait_queue+0x60/0x60 kthread+0xf5/0x130 ? try_to_merge_with_ksm_page+0x90/0x90 ? kthread_create_worker_on_cpu+0x70/0x70 ret_from_fork+0x1f/0x30 -------------------------------------------------------------------------- Fixes: e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with colouring") Signed-off-by: Muchun Song <songmuchun@bytedance.com> Signed-off-by: Xiongchun Duan <duanxiongchun@bytedance.com> --- Change in v2: Update commit message and patch subject. mm/ksm.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)