Greg Kroah-Hartman <gre...@linuxfoundation.org> writes: > On Thu, Nov 06, 2014 at 12:39:59PM +0100, Christian Riesch wrote: >> The current implementation of put_tty_queue() causes a race condition >> when re-arranged by the compiler. >> >> On my build with gcc 4.8.3, cross-compiling for ARM, the line >> >> *read_buf_addr(ldata, ldata->read_head++) = c; >> >> was re-arranged by the compiler to something like >> >> x = ldata->read_head >> ldata->read_head++ >> *read_buf_addr(ldata, x) = c; >> >> which causes a race condition. Invalid data is read if data is read >> before it is actually written to the read buffer. > > Really? A compiler can rearange things like that and expect things to > actually work? How is that valid?
This is actually required by the C spec. There is a sequence point before a function call, after the arguments have been evaluated. Thus all side-effects, such as the post-increment, must be complete before the function is called, just like in the example. There is no "re-arranging" here. The code is simply wrong. -- Måns Rullgård m...@mansr.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
