On Tue, 2009-04-28 at 06:27 +0200, Nick Piggin wrote: > On Sun, Apr 26, 2009 at 01:55:22PM -0400, Trond Myklebust wrote: > > On Sun, 2009-04-26 at 17:13 +0200, Nick Piggin wrote: > > > This doesn't seem to fix the race, though... on kernels with the > > > race still there, it will just open a window where you can have > > > a dirty pte but the page not written out. > > > > > > I don't understand. > > > > I'm just pointing out that the NFS client already calls > > __set_page_dirty_nobuffers() while holding the page lock inside the > > nfs_vm_page_mkwrite() call, so having the VM do it too in the call to > > set_page_dirty_balance() is actually redundant. IOW: as far as the NFS > > code is concerned, we can get rid of the ->set_page_dirty() callback in > > that situation. > > > > I couldn't find any other places in the VM code where we can have a > > dirty pte without also having called page_mkwrite() (and hence > > __set_page_dirty_nobuffers). As I said, adding a WARN_ON(!PageDirty()) > > in ->set_page_dirty() didn't ever trigger any cases where the > > set_page_dirty() was actually setting the dirty bit (except in the case > > where we race with page writeout in do_wp_page() and __do_fault()). > > > > That's why I believe disabling ->set_page_dirty() is safe here, and will > > in fact suffice to fix the page writeout race. > > Ah, no I don't think so because it opens another race where the > pte is dity but the page is marked clean. So how can that happen? AFAICS, when the pte is dirtied, we should get a page fault, which causes the page itself to be marked dirty by the nfs_vm_page_mkwrite() callback. When the page gets written out, the VM calls clear_page_dirty_for_io() which also causes the pte to be cleaned. At what point can you therefore have a situation where the pte is dirty without the page being marked as dirty too? -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
