Messages in this thread | | | Date | Fri, 1 Apr 2011 16:34:29 +0200 | Subject | Re: [PATCH] mm: fix possible cause of a page_mapped BUG | From | Robert Święcki <> |
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On Sat, Mar 19, 2011 at 6:34 AM, Hugh Dickins <hughd@google.com> wrote: > On Thu, 17 Mar 2011, Robert Swiecki wrote: >> On Tue, Mar 1, 2011 at 12:35 AM, Robert Swiecki <robert@swiecki.net> wrote: >> >> So, I compiled 2.6.38 and started fuzzing it. I'm bumping into other >> problems, and never seen anything about mremap in 2.6.38 (yet), > > Thanks a lot for getting back to this, Robert, and thanks for the update. > I won't be celebrating, but this sounds like good news for my mremap patch. > >> as it had been happening in 2.6.37-rc2. The output goes to >> http://alt.swiecki.net/linux_kernel/ - I'm still trying. > > A problem in sys_mlock: I've Cc'ed Michel who is the current expert. > > A problem in sys_munlock: Michel again, except vma_prio_tree_add is > implicated, and I used to be involved with that. I've appended below > a debug patch which I wrote years ago, and have largely forgotten, but > Andrew keeps it around in mmotm: we might learn more if you add that > into your kernel build.
Hey, I'll apply your patch and check it out. In the meantime I triggered another Oops (NULL-ptr deref via sys_mprotect).
The oops is here:
http://alt.swiecki.net/linux_kernel/sys_mprotect-2.6.38.txt
> A problem in next_pidmap from find_ge_pid from ... proc_pid_readdir. > I did spend a while looking into that when you first reported it. > I'm pretty sure, from the register values, that it's a result of > a pid number (in some places signed int, in some places unsigned) > getting unexpectedly sign-extended to negative, so indexing before > the beginning of an array; but I never tracked down the root of the > problem, and failed to reproduce it with odd lseeks on the directory. > > Ah, the one you report now comes from compat_sys_getdents, > whereas the original one came from compat_sys_old_readdir: okay, > I had been wondering whether it was peculiar to the old_readdir case, > but no, it's reproduced with getdents too. Might be peculiar to compat. > > Anyway, I've Cc'ed Eric who will be the best for that one. > > And a couple of watchdog problems: I haven't even glanced at > those, hope someone else can suggest a good way forward on them. > > Hugh > >> >> > Btw, the fuzzer is here: http://code.google.com/p/iknowthis/ >> > >> > I think i was trying it with this revision: >> > http://code.google.com/p/iknowthis/source/detail?r=11 (i386 mode, >> > newest 'iknowthis' supports x86-64 natively), so feel free to try it. >> > >> > It used to crash the machine (it's BUG_ON but the system became >> > unusable) in matter of hours. Btw, when I was testing it for the last >> > time it Ooopsed much more frequently in proc_readdir (I sent report in >> > one of earliet e-mails). > > From: Hugh Dickins <hughd@google.com> > > Jayson Santos has sighted mm/prio_tree.c:78,79 BUGs (kernel bugzilla 8446), > and one was sighted a couple of years ago. No reason yet to suppose > they're prio_tree bugs, but we can't tell much about them without seeing > the vmas. > > So dump vma and the one it's supposed to resemble: I had expected to use > print_hex_dump(), but that's designed for u8 dumps, whereas almost every > field of vm_area_struct is either a pointer or an unsigned long - which > look nonsense dumped as u8s. > > Replace the two BUG_ONs by a single WARN_ON; and if it fires, just keep > this vma out of the tree (truncation and swapout won't be able to find it). > How safe this is depends on what the error really is; but we hold a file's > i_mmap_lock here, so it may be impossible to recover from BUG_ON. > > Signed-off-by: Hugh Dickins <hughd@google.com> > Cc: Jayson Santos <jaysonsantos2003@yahoo.com.br> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > --- > > mm/prio_tree.c | 33 ++++++++++++++++++++++++++++----- > 1 file changed, 28 insertions(+), 5 deletions(-) > > diff -puN mm/prio_tree.c~prio_tree-debugging-patch mm/prio_tree.c > --- a/mm/prio_tree.c~prio_tree-debugging-patch > +++ a/mm/prio_tree.c > @@ -67,6 +67,20 @@ > * vma->shared.vm_set.head == NULL ==> a list node > */ > > +static void dump_vma(struct vm_area_struct *vma) > +{ > + void **ptr = (void **) vma; > + int i; > + > + printk("vm_area_struct at %p:", ptr); > + for (i = 0; i < sizeof(*vma)/sizeof(*ptr); i++, ptr++) { > + if (!(i & 3)) > + printk("\n"); > + printk(" %p", *ptr); > + } > + printk("\n"); > +} > + > /* > * Add a new vma known to map the same set of pages as the old vma: > * useful for fork's dup_mmap as well as vma_prio_tree_insert below. > @@ -74,14 +88,23 @@ > */ > void vma_prio_tree_add(struct vm_area_struct *vma, struct vm_area_struct *old) > { > - /* Leave these BUG_ONs till prio_tree patch stabilizes */ > - BUG_ON(RADIX_INDEX(vma) != RADIX_INDEX(old)); > - BUG_ON(HEAP_INDEX(vma) != HEAP_INDEX(old)); > - > vma->shared.vm_set.head = NULL; > vma->shared.vm_set.parent = NULL; > > - if (!old->shared.vm_set.parent) > + if (WARN_ON(RADIX_INDEX(vma) != RADIX_INDEX(old) || > + HEAP_INDEX(vma) != HEAP_INDEX(old))) { > + /* > + * This should never happen, yet it has been seen a few times: > + * we cannot say much about it without seeing the vma contents. > + */ > + dump_vma(vma); > + dump_vma(old); > + /* > + * Don't try to link this (corrupt?) vma into the (corrupt?) > + * prio_tree, but arrange for its removal to succeed later. > + */ > + INIT_LIST_HEAD(&vma->shared.vm_set.list); > + } else if (!old->shared.vm_set.parent) > list_add(&vma->shared.vm_set.list, > &old->shared.vm_set.list); > else if (old->shared.vm_set.head) >
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