APPLIED/cmnt: [X][X/linux-kvm][SRU][PATCH 0/1] mm: mlock: avoid increase mm->locked_vm on mlock() when already mlock2(, MLOCK_ONFAULT)
khalid.elmously at canonical.com
Thu Nov 8 06:49:38 UTC 2018
Applied to xenial/master-next only
On 2018-10-23 16:44:51 , Po-Hsu Lin wrote:
> BugLink: https://bugs.launchpad.net/bugs/1793451
> == Justification ==
> When one vma was with flag VM_LOCKED|VM_LOCKONFAULT (by invoking
> mlock2(,MLOCK_ONFAULT)), it can again be populated with mlock() with
> VM_LOCKED flag only.
> There is a hole in mlock_fixup() which increase mm->locked_vm twice even
> the two operations are on the same vma and both with VM_LOCKED flags.
> The issue can be reproduced by following code:
> mlock2(p, 1024 * 64, MLOCK_ONFAULT); //VM_LOCKED|VM_LOCKONFAULT
> mlock(p, 1024 * 64); //VM_LOCKED
> Then check the increase VmLck field in /proc/pid/status(to 128k).
> When vma is set with different vm_flags, and the new vm_flags is with
> VM_LOCKED, it is not necessarily be a "new locked" vma.
> There is a dedicated reproducer, the "mlock203" test in ubuntu_ltp_syscalls, you can see the failure for all the Ubuntu 4.4 kernel:
> tag=mlock203 stime=1537369891
> tst_test.c:1063: INFO: Timeout per run is 0h 05m 00s
> mlock203.c:63: FAIL: Locking one memory again increased VmLck
> passed 0
> failed 1
> skipped 0
> warnings 0
> == Fix ==
> b155b4fd (mm: mlock: avoid increase mm->locked_vm on mlock() when already mlock2(,MLOCK_ONFAULT))
> A test kernel for Xenial / Xenial-KVM could be found here:
> == Regression Potential ==
> Low, this patch prevents mm->locked_vm from increment just by adding an extra check to see if the old vm_flags is already VM_LOCKED.
> == Test Case ==
> Run the mlock203 test in ubuntu_ltp_syscalls test suite. And it will pass with the patched kernel.
> Simon Guo (1):
> mm: mlock: avoid increase mm->locked_vm on mlock() when already
> mm/mlock.c | 3 +++
> 1 file changed, 3 insertions(+)
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