On Thu, 11 Feb 2016, Kirill A. Shutemov wrote: > On Thu, Feb 11, 2016 at 09:09:42PM +0200, Kirill A. Shutemov wrote: > > On Thu, Feb 11, 2016 at 07:22:23PM +0100, Gerald Schaefer wrote: > > > Hi, > > > > > > Sebastian Ott reported random kernel crashes beginning with v4.5-rc1 and > > > he also bisected this to commit 61f5d698 "mm: re-enable THP". Further > > > review of the THP rework patches, which cannot be bisected, revealed > > > commit fecffad "s390, thp: remove infrastructure for handling splitting PMDs" > > > (and also similar commits for other archs). > > > > > > This commit removes the THP splitting bit and also the architecture > > > implementation of pmdp_splitting_flush(), which took care of the IPI for > > > fast_gup serialization. The commit message says > > > > > > pmdp_splitting_flush() is not needed too: on splitting PMD we will do > > > pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as > > > needed for fast_gup > > > > > > The assumption that a TLB flush will also produce an IPI is wrong on s390, > > > and maybe also on other architectures, and I thought that this was actually > > > the main reason for having an arch-specific pmdp_splitting_flush(). > > > > > > At least PowerPC and ARM also had an individual implementation of > > > pmdp_splitting_flush() that used kick_all_cpus_sync() instead of a TLB > > > flush to send the IPI, and those were also removed. Putting the arch > > > maintainers and mailing lists on cc to verify. > > > > > > On s390 this will break the IPI serialization against fast_gup, which > > > would certainly explain the random kernel crashes, please revert or fix > > > the pmdp_splitting_flush() removal. > > > > Sorry for that. > > > > I believe, the problem was already addressed for PowerPC: > > > > http://lkml.kernel.org/g/454980831-16631-1-git-send-email-aneesh.kumar@xxxxxxxxxxxxxxxxxx > > Correct link is > > http://lkml.kernel.org/g/1454980831-16631-1-git-send-email-aneesh.kumar@xxxxxxxxxxxxxxxxxx > Based on your suggestion Gerald provided the following patch but sadly it didn't fix the problem. Sebastian --- arch/s390/include/asm/pgtable.h | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/s390/include/asm/pgtable.h +++ b/arch/s390/include/asm/pgtable.h @@ -1587,6 +1587,8 @@ static inline void pmdp_invalidate(struc unsigned long address, pmd_t *pmdp) { pmdp_flush_direct(vma->vm_mm, address, pmdp); + /* Serialize against fast_gup with IPI */ + kick_all_cpus_sync(); } #define __HAVE_ARCH_PMDP_SET_WRPROTECT -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>