On 04/06, Hugh Dickins wrote: > > I've long detested that behaviour of GUP write,force, and my strong > preference would be not to layer more strangeness upon strangeness, > but limit the damage by making GUP write,force fail in that case, > instead of inserting a PageAnon page into a VM_SHARED mapping. > > I think it's unlikely that it will cause a regression in real life > (it already fails if you did not open the mmap'ed file for writing), Yes, and this is what looks confusing to me. Assuming I understand you (and the code) correctly ;) If we have a (PROT_READ, MAP_SHARED) file mapping, then FOLL_FORCE works depending on "file->f_mode & FMODE_WRITE". Afaics, because do_mmap_pgoff(MAP_SHARED) clears VM_MAYWRITE if !FMODE_WRITE, and gup(FORCE) checks "vma->vm_flags & VM_MAYWRITE" before follow_page/etc. OTOH, if the file was opened without FMODE_WRITE, then I do not really understand how (PROT_READ, MAP_SHARED) differs from (PROT_READ, MAP_PRIVATE). However, in the latter case FOLL_FORCE works, VM_MAYWRITE was not cleared. Speaking of the difference above, I'd wish I could understand what VM_MAYSHARE actually means except "MAP_SHARED was used". Oleg. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>