Messages in this thread Patch in this message | | | Subject | Re: mbind() breaks its API definition since v5.2 by commit d883544515aa (mm: mempolicy: make the behavior consistent when MPOL_MF_MOVE* and MPOL_MF_STRICT were specified) | From | Yang Shi <> | Date | Tue, 29 Oct 2019 21:32:54 -0700 |
| |
On 10/29/19 8:12 PM, Li Xinhai wrote: > On 2019-10-30 at 10:50 Yang Shi wrote: >> >> On 10/29/19 7:27 PM, Li Xinhai wrote: >>> One change in do_mbind() of this commit has suspicious usage of return value of >>> queue_pages_range(), excerpt as below: >>> >>> --- >>> @@ -1243,10 +1265,15 @@ static long do_mbind(unsigned long start, unsigned long len, >>> if (err) >>> goto mpol_out; >>> >>> - err = queue_pages_range(mm, start, end, nmask, >>> + ret = queue_pages_range(mm, start, end, nmask, >>> flags | MPOL_MF_INVERT, &pagelist); >>> - if (!err) >>> - err = mbind_range(mm, start, end, new); >>> + >>> + if (ret < 0) { /////// convert to all possible 'ret' to '-EIO' <<<< >>> + err = -EIO; >>> + goto up_out; >>> + } >>> + >>> + err = mbind_range(mm, start, end, new); >>> >>> if (!err) { >>> int nr_failed = 0; >>> --- >>> >>> Note that inside queue_pages_range(), the call to walk_page_range() may return >>> errors from 'test_walk' of 'struct mm_walk_ops', e.g. -EFAULT. Now, those error >>> codes are no longer reported to user space application. >>> >>> From user space, the mbind() call need to reported error, with EFAULT, as example: >>> EFAULT >>> Part or all of the memory range specified by nodemask and maxnode points >>> outside your accessible address space. Or, there was an unmapped hole in the >>> specified memory range specified by addr and len. >> Thanks for catching this. That commit was aimed to correct the return >> values for some corner cases in mbind(), but it should not alter the >> errno for other failure cases, i.e. -EFAULT. >> >> Could you please try the below patch (build test only)? >> >> diff --git a/mm/mempolicy.c b/mm/mempolicy.c >> index 4ae967b..99df43a 100644 >> --- a/mm/mempolicy.c >> +++ b/mm/mempolicy.c >> @@ -1286,7 +1286,7 @@ static long do_mbind(unsigned long start, unsigned >> long len, >> flags | MPOL_MF_INVERT, &pagelist); >> >> if (ret < 0) { >> - err = -EIO; >> + err = ret; >> goto up_out; >> } >> >> > This seems do not work, because the 'pagelist' would have some pages queued > into it, need to put back those pages instead of return quickly. > > So, we need to remove this page leak as well. <<<<<< > > In my understanding, revert the changes as I quoted above may solve it, but not sure > the details about changes at end of do_mbind(), should keep them at there without > further change?
Thanks for pointing this out. We don't have to revert this commit to handle the non-empty pagelist correctly. The simplest way is to just put those pages back and I'm supposed this is also the preferred way since mbind_range() is not called to really apply the policy so those pages should not be migrated.
The below patch should solve this:
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 4ae967b..d80025c 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1286,7 +1286,10 @@ static long do_mbind(unsigned long start, unsigned long len, flags | MPOL_MF_INVERT, &pagelist);
if (ret < 0) { - err = -EIO; + if (!list_empty(&pagelist)) + putback_movable_pages(&pagelist); + + err = ret; goto up_out; }
> - Xinhai > >>> Please correct me if this is the intended change(and will have updated API >>> definition), or something was misunderstood. >>> >>> -Xinhai > >
| |