On Fri, 13 Mar 2009, Nick Piggin wrote: > On Thu, Mar 12, 2009 at 04:03:57PM -0700, Sage Weil wrote: > > On Thu, 12 Mar 2009, Trond Myklebust wrote: > > > On Wed, 2009-03-11 at 04:55 +0100, Nick Piggin wrote: > > > > page_mkwrite is called with neither the page lock nor the ptl held. This > > > > means a page can be concurrently truncated or invalidated out from underneath > > > > it. Callers are supposed to prevent truncate races themselves, however > > > > previously the only thing they can do in case they hit one is to raise a > > > > SIGBUS. A sigbus is wrong for the case that the page has been invalidated > > > > or truncated within i_size (eg. hole punched). Callers may also have to > > > > perform memory allocations in this path, where again, SIGBUS would be wrong. > > > > > > > > The previous patch made it possible to properly specify errors. Convert > > > > the generic buffer.c code and btrfs to return sane error values > > > > (in the case of page removed from pagecache, VM_FAULT_NOPAGE will cause the > > > > fault handler to exit without doing anything, and the fault will be retried > > > > properly). > > > > > > > > This fixes core code, and converts btrfs as a template/example. All other > > > > filesystems defining their own page_mkwrite should be fixed in a similar > > > > manner. > > > > > > There appears to be another atomicity problem in the same area of > > > code... > > > > > > The lack of locking between the call to ->page_mkwrite() and the > > > subsequent call to set_page_dirty_balance() means that the filesystem > > > may actually already have written out the page by the time you get round > > > to calling set_page_dirty_balance(). > > > > We were just banging our heads against this issue last week. > > That's coming too: > http://marc.info/?l=linux-fsdevel&m=123555461816471&w=2 > > (we ended up deciding to call with page unlocked and return with locked, > as it solves locking problems in some filesystems). > > I'll resend that patch soonish. Hopefully it will work for you two? Yeah, that'll work nicely. Thanks! sage -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
