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    SubjectRe: [BUG] Invalid return address of mmap() followed by mbind() in multithreaded context
    (2011/06/28 2:18), Kornilios Kourtis wrote:
    >
    > Hi,
    >
    > On Fri, Jun 17, 2011 at 06:21:49PM +0300, Vasileios Karakasis wrote:
    >> Hi,
    >>
    >> I am implementing a multithreaded numa aware code where each thread
    >> mmap()'s an anonymous private region and then mbind()'s it to its local
    >> node. The threads are performing a series of such mmap() + mbind()
    >> operations. My program crashed with SIGSEGV and I noticed that mmap()
    >> returned an invalid address.
    >
    > I've taken a closer look at this issue.
    >
    > As Vasileios said, it can be reproduced by having two threads doing the
    > following loop:
    > | for {
    > | addr = mmap(4096, MAP_ANONUMOUS)
    > | if (addr == (void *)-1)
    > | continue
    > | mbind(addr, 4096, 0x1) // do mbind on first NUMA node
    > | }
    > After a couple of iterations, mbind() will return EFAULT, although the addr is
    > valid.
    >
    > Doing a bisect, pins it down to the following commit (Author added to To:):
    > 9d8cebd4bcd7c3878462fdfda34bbcdeb4df7ef4
    > mm: fix mbind vma merge problem
    > Which adds merging of vmas in the mbind() path.
    > Reverting this commit, seems to fix the issue.
    >
    > I 've added some printks to track down the issue, and EFAULT is returned on:
    > mm/mempolicy.c: mbind_range()
    > | vma = find_vma_prev(mm. start, &prev);
    > | if (!vma |vma->vm_start > start)
    > | return EFAULT;
    > Where: vma->start > start
    >
    > I am not sure what exactly happens, but concurrent merges and splits
    > of (already mapped) VMAs do not seem to work well together.

    Hi

    Thank you for digging this! I look it at soon as far as possible.

    - kosaki



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