Messages in this thread | | | Date | Mon, 12 Mar 2007 13:14:47 +0100 | From | Nick Piggin <> | Subject | Re: [PATCH 2/2] mm: incorrect direct io error handling (v6) |
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On Mon, Mar 12, 2007 at 12:23:00PM +0300, Dmitriy Monakhov wrote: > Nick Piggin <npiggin@suse.de> writes: > > > On Mon, Mar 12, 2007 at 11:55:30AM +0300, Dmitriy Monakhov wrote: > >> Nick Piggin <npiggin@suse.de> writes: > >> > >> > On Mon, Mar 12, 2007 at 10:58:10AM +0300, Dmitriy Monakhov wrote: > > > >> >> @@ -2240,6 +2241,29 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov, > >> >> mutex_lock(&inode->i_mutex); > >> >> ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs, > >> >> &iocb->ki_pos); > >> >> + /* > >> >> + * If __generic_file_aio_write_nolock has failed. > >> >> + * This may happen because of: > >> >> + * 1) Bad segment found (failed before actual write attempt) > >> >> + * 2) Segments are good, but actual write operation failed > >> >> + * and may have instantiated a few blocks outside i_size. > >> >> + * a) in case of buffered write these blocks was already > >> >> + * trimmed by generic_file_buffered_write() > >> >> + * b) in case of O_DIRECT these blocks weren't trimmed yet. > >> >> + * > >> >> + * In case of (2b) these blocks have to be trimmed off again. > >> >> + */ > >> >> + if (unlikely( ret < 0 && file->f_flags & O_DIRECT)) { > >> >> + unsigned long nr_segs_avail = nr_segs; > >> >> + size_t count = 0; > >> >> + if (!generic_segment_checks(iov, &nr_segs_avail, &count, > >> >> + VERIFY_READ)) { > >> >> + /*It is (2b) case, because segments are good*/ > >> >> + loff_t isize = i_size_read(inode); > >> >> + if (pos + count > isize) > >> >> + vmtruncate(inode, isize); > >> >> + } > >> >> + } > >> > > >> > OK, but wouldn't this be better to be done in the actual direct IO > >> > functions themselves? Thus you could be sure that you have the 2b case, > >> > and the code would be less fragile to something changing? > >> Ohh, We can't just call vmtruncate() after generic_file_direct_write() > >> failure while __generic_file_aio_write_nolock() becase where is no guarantee > >> what i_mutex held. In fact all existing fs always invoke > >> __generic_file_aio_write_nolock() with i_mutex held in case of S_ISREG files, > >> but this was't explicitly demanded and documented. I've proposed to do it in > >> previous versions of this patch, because it this just document current state > >> of affairs, but David Chinner wasn't agree with it. > > > > It seemed like it was documented in the comments that you altered in this > > patch... > > > > How would such a filesystem that did not hold i_mutex propose to fix the > > problem? > > > > The burden should be on those filesystems that might not want to hold > > i_mutex here, to solve the problem nicely, rather than generic code to take > > this ugly code. > Ok then what do you think about this version http://lkml.org/lkml/2006/12/18/103 > witch was posted almost month ago :)
That seems better, but people might take issue with the fact that it has to make the check for S_ISREG files. I don't know... people with more knowledge of the vfs+fs side of things might have better input.
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