David Chinner <[EMAIL PROTECTED]> writes: > On Mon, Dec 18, 2006 at 04:22:44PM +0300, Dmitriy Monakhov wrote: >> diff --git a/mm/filemap.c b/mm/filemap.c >> index 8332c77..7c571dd 100644 >> --- a/mm/filemap.c >> +++ b/mm/filemap.c >> @@ -2044,8 +2044,9 @@ generic_file_direct_write(struct kiocb * >> /* >> * Sync the fs metadata but not the minor inode changes and >> * of course not the data as we did direct DMA for the IO. >> - * i_mutex is held, which protects generic_osync_inode() from >> - * livelocking. AIO O_DIRECT ops attempt to sync metadata here. >> + * i_mutex may not being held (XFS does this), if so some specific >> locking >> + * ordering must protect generic_osync_inode() from livelocking. >> + * AIO O_DIRECT ops attempt to sync metadata here. >> */ >> if ((written >= 0 || written == -EIOCBQUEUED) && >> ((file->f_flags & O_SYNC) || IS_SYNC(inode))) { >> @@ -2279,6 +2280,17 @@ __generic_file_aio_write_nolock(struct k >> >> written = generic_file_direct_write(iocb, iov, &nr_segs, pos, >> ppos, count, ocount); >> + /* >> + * If host is not S_ISBLK generic_file_direct_write() may >> + * have instantiated a few blocks outside i_size files >> + * Trim these off again. >> + */ >> + if (unlikely(written < 0) && !S_ISBLK(inode->i_mode)) { >> + loff_t isize = i_size_read(inode); >> + if (pos + count > isize) >> + vmtruncate(inode, isize); >> + } >> + >> if (written < 0 || written == count) >> goto out; > > You comment in the first hunk that i_mutex may not be held here, > but there's no comment in __generic_file_aio_write_nolock() that the > i_mutex must be held for !S_ISBLK devices. Any one may call directly call generic_file_direct_write() with i_mutex not held. > >> @@ -2341,6 +2353,13 @@ ssize_t generic_file_aio_write_nolock(st >> ssize_t ret; >> >> BUG_ON(iocb->ki_pos != pos); >> + /* >> + * generic_file_buffered_write() may be called inside >> + * __generic_file_aio_write_nolock() even in case of >> + * O_DIRECT for non S_ISBLK files. So i_mutex must be held. >> + */ >> + if (!S_ISBLK(inode->i_mode)) >> + BUG_ON(!mutex_is_locked(&inode->i_mutex)); >> >> ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs, >> &iocb->ki_pos); > > I note that you comment here in generic_file_aio_write_nolock(), > but it's not immediately obvious that this is refering to the > vmtruncate() call in __generic_file_aio_write_nolock(). This is not about vmtruncate(). __generic_file_aio_write_nolock() may call generic_file_buffered_write() even in case of O_DIRECT for !S_ISBLK, and generic_file_buffered_write() has documented locking rules (i_mutex held). IMHO it is important to explicitly document this . And after we realize that i_mutex always held, vmtruncate() may be safely called. > > IOWs, wouldn't it be better to put this comment and check in > __generic_file_aio_write_nolock() directly above the vmtruncate() > call that cares about this? > >> @@ -2383,8 +2402,8 @@ ssize_t generic_file_aio_write(struct ki >> EXPORT_SYMBOL(generic_file_aio_write); >> >> /* >> - * Called under i_mutex for writes to S_ISREG files. Returns -EIO if >> something >> - * went wrong during pagecache shootdown. >> + * May be called without i_mutex for writes to S_ISREG files. XFS does this. >> + * Returns -EIO if something went wrong during pagecache shootdown. >> */ > > Not sure you need to say "XFS does this" - other filesystems may do this > in the future..... Yes, but where are multiple comments about "reiserfs does this" in fs/buffer.c
> > Cheers, > > Dave. > -- > Dave Chinner > Principal Engineer > SGI Australian Software Group > - > 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/ - 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/