On Wed, Mar 29, 2023 at 2:53 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, 29 Mar 2023 18:53:30 +0400 Ivan Orlov <ivan.orlov0322@xxxxxxxxx> wrote: > > > Syzkaller reported the following issue: > > > > ... > > > > The 'xas_store' call during page cache scanning can potentially > > translate 'xas' into the error state (with the reproducer provided > > by the syzkaller the error code is -ENOMEM). However, there are no > > further checks after the 'xas_store', and the next call of 'xas_next' > > at the start of the scanning cycle doesn't increase the xa_index, > > and the issue occurs. > > > > This patch will add the xarray state error checking after the > > 'xas_store' and the corresponding result error code. > > > > Tested via syzbot. > > > > Reported-by: syzbot+9578faa5475acb35fa50@xxxxxxxxxxxxxxxxxxxxxxxxx > > Link: https://syzkaller.appspot.com/bug?id=7d6bb3760e026ece7524500fe44fb024a0e959fc > > Signed-off-by: Ivan Orlov <ivan.orlov0322@xxxxxxxxx> > > --- > > mm/khugepaged.c | 10 ++++++++++ > > 1 file changed, 10 insertions(+) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index 92e6f56a932d..4d9850d9ea7f 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -55,6 +55,7 @@ enum scan_result { > > SCAN_CGROUP_CHARGE_FAIL, > > SCAN_TRUNCATED, > > SCAN_PAGE_HAS_PRIVATE, > > + SCAN_STORE_FAILED, > > }; > > > > #define CREATE_TRACE_POINTS > > @@ -1840,6 +1841,15 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr, > > goto xa_locked; > > } > > xas_store(&xas, hpage); > > + if (xas_error(&xas)) { > > + /* revert shmem_charge performed > > + * in the previous condition > > + */ > > + mapping->nrpages--; > > + shmem_uncharge(mapping->host, 1); > > + result = SCAN_STORE_FAILED; > > + goto xa_locked; > > + } > > nr_none++; > > continue; > > } > > Needs this, I assume. > > --- a/include/trace/events/huge_memory.h~mm-khugepaged-fix-kernel-bug-in-hpage_collapse_scan_file-fix > +++ a/include/trace/events/huge_memory.h > @@ -36,7 +36,8 @@ > EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \ > EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \ > EM( SCAN_TRUNCATED, "truncated") \ > - EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ > + EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ > + EMe(SCAN_STORE_FAILED, "store_failed") I'm a little bit reluctant to make the error code list longer, can we just return SCAN_FAIL? IIUC this issue should happen very rarely, maybe not worth a new error code. Basically the rollback approach makes sense to me. IIRC Zach was looking into the same problem, loop him in. He may share some thoughts. > > #undef EM > #undef EMe > _ > >
