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 I think kick_all_cpus_sync() in arch-specific pmdp_invalidate() would do the trick, right? If yes, I'll prepare patch tomorrow (some sleep required). -- Kirill A. Shutemov -- 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>