arch: mm: remove obsolete init OOM protection

The memcg code can trap tasks in the context of the failing allocation
until an OOM situation is resolved.  They can hold all kinds of locks
(fs, mm) at this point, which makes it prone to deadlocking.

This series converts memcg OOM handling into a two step process that is
started in the charge context, but any waiting is done after the fault
stack is fully unwound.

Patches 1-4 prepare architecture handlers to support the new memcg
requirements, but in doing so they also remove old cruft and unify
out-of-memory behavior across architectures.

Patch 5 disables the memcg OOM handling for syscalls, readahead, kernel
faults, because they can gracefully unwind the stack with -ENOMEM.  OOM
handling is restricted to user triggered faults that have no other
option.

Patch 6 reworks memcg's hierarchical OOM locking to make it a little
more obvious wth is going on in there: reduce locked regions, rename
locking functions, reorder and document.

Patch 7 implements the two-part OOM handling such that tasks are never
trapped with the full charge stack in an OOM situation.

This patch:

Back before smart OOM killing, when faulting tasks were killed directly on
allocation failures, the arch-specific fault handlers needed special
protection for the init process.

Now that all fault handlers call into the generic OOM killer (see commit
609838cfed97: "mm: invoke oom-killer from remaining unconverted page
fault handlers"), which already provides init protection, the
arch-specific leftovers can be removed.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: azurIt <azurit@pobox.sk>
Acked-by: Vineet Gupta <vgupta@synopsys.com>	[arch/arc bits]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index 0fd1f0d515ffb394f64107ceb1ecdfb856a8858d..6b0bb415af40ff7264a62176c224eca181d4e1d4 100644 (file)
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -122,7 +122,6 @@ good_area:
                        goto bad_area;
        }
 
-survive:
        /*
         * If for any reason at all we couldn't handle the fault,
         * make sure we exit gracefully rather than endlessly redo
@@ -201,10 +200,6 @@ no_context:
        die("Oops", regs, address);
 
 out_of_memory:
-       if (is_global_init(tsk)) {
-               yield();
-               goto survive;
-       }
        up_read(&mm->mmap_sem);
 
        if (user_mode(regs)) {

diff --git a/arch/score/mm/fault.c b/arch/score/mm/fault.c
index 6b18fb0189ae4ff0d06fea13b717b42a8f58c664..4b71a626d41e8196b3fe1dd7ed9cad750ee560b6 100644 (file)
--- a/arch/score/mm/fault.c
+++ b/arch/score/mm/fault.c
@@ -100,7 +100,6 @@ good_area:
                        goto bad_area;
        }
 
-survive:
        /*
        * If for any reason at all we couldn't handle the fault,
        * make sure we exit gracefully rather than endlessly redo
@@ -167,11 +166,6 @@ no_context:
        */
 out_of_memory:
        up_read(&mm->mmap_sem);
-       if (is_global_init(tsk)) {
-               yield();
-               down_read(&mm->mmap_sem);
-               goto survive;
-       }
        if (!user_mode(regs))
                goto no_context;
        pagefault_out_of_memory();

diff --git a/arch/tile/mm/fault.c b/arch/tile/mm/fault.c
index 111d5a9b76f146c541d4fb17d56aacead9e7782d..4fd2c0f2a66dc847698c98082df6396c44cf01ba 100644 (file)
--- a/arch/tile/mm/fault.c
+++ b/arch/tile/mm/fault.c
@@ -430,7 +430,6 @@ good_area:
                        goto bad_area;
        }
 
- survive:
        /*
         * If for any reason at all we couldn't handle the fault,
         * make sure we exit gracefully rather than endlessly redo
@@ -555,11 +554,6 @@ no_context:
  */
 out_of_memory:
        up_read(&mm->mmap_sem);
-       if (is_global_init(tsk)) {
-               yield();
-               down_read(&mm->mmap_sem);
-               goto survive;
-       }
        if (is_kernel_mode)
                goto no_context;
        pagefault_out_of_memory();