> Quoting Linus Torvalds <[EMAIL PROTECTED]>: > Subject: Re: [PATCH] mm: fix page_mkclean_one (was: 2.6.19 file content > corruption on ext3) > > Peter, tell me I'm crazy, but with the new rules, the following condition > is a bug: > > - shared mapping > - writable > - not already marked dirty in the PTE > > because that combination means that the hardware can mark the PTE dirty > without us even realizing (and thus not marking the "struct page *" > dirty).
Er. Sorry about bumping in, and I'm not sure I understand all of the discussion, but this reminded me of an old issue with COW that created what looks like a vaguely similiar data corruption on infiniband. We solved this for infiniband with MADV_DONTFORK, but I always wondered why does it not affect other parts of kernel. Small reminder from that discussion: down mmap sem get user pages up mmap sem page becomes shared, and COW (e.g. fork) process writes to first byte of page <----- gets a copy Now we had a problem: struct page that we got from get user pages does not point to a correct page in our process. For example: if at some point we map this page for DMA, and hardware writes to last byte of page -----> process does not see this data. So for infiniband, what we do is a combination of - prevent page from becoming COW while hardware might DMA to this page, and - ask users not to write to page if hardware might DMA to same page (even if its using different bytes). I just wandered - is there some chance something like this could be happening in the fs code? HTH, -- MST - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
