On 06/21/2017 08:31 PM, Oleg Nesterov wrote:
On 06/21, Dmitry Safonov wrote:
The only question I have - how is it connected to guard page?
Because with stack guard page do_page_fault() almost never needs to
call expand_stack(), thus this check was almost never tested, I guess.
Probably it should go away now.
I'll write the changelog and patch tomorrow, unless someone does this
before.
Ugh, maybe it's also worth now to update man 2 mmap.
At this moment, mmap() will no more return address one page lower
and "guard" is no more a page:
MAP_GROWSDOWN
This flag is used for stacks. It indicates to the kernel virtual
memory system that the mapping should extend downward in
memory. The return address is one page lower than the memory
area that is actually created in the process's virtual address
space. Touching an address in the "guard" page below the mapping
will cause the mapping to grow by a page. This growth can be
repeated until the mapping grows to within a page of the high end
of the next lower mapping, at which point touching the "guard"
page will result in a SIGSEGV signal.
CC'ing Michael
--
Dmitry
