Re: [PATCH 01/18] mm: Make mmap_sem for write waits killable for mm syscalls

From: Vlastimil Babka
Date: Thu Mar 10 2016 - 10:47:33 EST

On 02/29/2016 02:26 PM, Michal Hocko wrote:
From: Michal Hocko <mhocko@xxxxxxxx>

This is the first step in making mmap_sem write holders killable. It


focuses on the trivial ones which are taking the lock early after
entering the syscall and they are not changing state before.

Therefore it is very easy to change them to use down_write_killable
and immediately return with -EINTR. This will allow the waiter to
pass away without blocking the mmap_sem which might be required to
make a forward progress. E.g. the oom reaper will need the lock for
reading to dismantle the OOM victim address space.

The only tricky function in this patch is vm_mmap_pgoff which has many
call sites via vm_mmap. To reduce the risk keep vm_mmap with the
original non-killable semantic for now.

vm_munmap callers do not bother checking the return value so open code
it into the munmap syscall path for now for simplicity.

Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>