On 09/10/19, 6:43 PM, "Vlastimil Babka" <vbabka@xxxxxxx> wrote: >> Reported-by: Jann Horn <jannh@xxxxxxxxxx> >> Acked-by: Matthew Wilcox <willy@xxxxxxxxxxxxx> >> Cc: stable@xxxxxxxxxx >> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> >> [ 4.4.y backport notes: >> Ajay: Added local variable 'err' with-in follow_hugetlb_page() >> from 2be7cfed995e, to resolve compilation error >> Srivatsa: Replaced call to get_page_foll() with try_get_page_foll() ] >> Signed-off-by: Srivatsa S. Bhat (VMware) <srivatsa@xxxxxxxxxxxxx> >> Signed-off-by: Ajay Kaher <akaher@xxxxxxxxxx> >> --- >> mm/gup.c | 43 ++++++++++++++++++++++++++++++++----------- >> mm/hugetlb.c | 16 +++++++++++++++- >> 2 files changed, 47 insertions(+), 12 deletions(-) > > This seems to have the same issue as the 4.9 stable version [1], in not > touching the arch-specific gup.c variants. > > [1] > https://lore.kernel.org/lkml/6650323f-dbc9-f069-000b-f6b0f941a065@xxxxxxx/ Thanks Vlastimil for highlighting this here. Yes, arch-specific gup.c variants also need to handle not only for 4.4.y, however it should be handled till 4.19.y. I believe it's better to start from 4.19.y and then backport those changes till 4.4.y. Affected areas of gup.c (where page->count have been used) are: #1: get_page() used in these files and this is safe as it's defined in mm.h (here it's already taken care of) #2: get_head_page_multiple() has following: VM_BUG_ON_PAGE(page_count(page) == 0, page); Need to change this to: VM_BUG_ON_PAGE(page_ref_zero_or_close_to_overflow(page), page); #3: Some of the files have used page_cache_get_speculative(), page_cache_add_speculative() with combination of compound_head(), this scenario needs to be handled as it was handled here: https://lore.kernel.org/stable/1570581863-12090-7-git-send-email-akaher@xxxxxxxxxx/ Please share with me any suggestions or patches if you have already worked on this. Could we handle arch-specific gup.c in different patch sets and let these patches to merge to 4.4.y? - Ajay
