Re: [PATCH] uprobes: wait for mmap_sem for write killable

From: Vlastimil Babka
Date: Fri Mar 11 2016 - 09:58:57 EST

On 02/29/2016 06:42 PM, Michal Hocko wrote:
From: Michal Hocko <mhocko@xxxxxxxx>

xol_add_vma needs mmap_sem for write. If the waiting task gets killed by
the oom killer it would block oom_reaper from asynchronous address space
reclaim and reduce the chances of timely OOM resolving. Wait for the
lock in the killable mode and return with EINTR if the task got killed
while waiting.

Do not warn in dup_xol_work if __create_xol_area failed due to fatal
signal pending because this is usually considered a kernel issue.

Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
kernel/events/uprobes.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 8eef5f55d3f0..fb4a6bcc88ce 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1130,7 +1130,9 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
struct vm_area_struct *vma;
int ret;

- down_write(&mm->mmap_sem);
+ if (down_write_killable(&mm->mmap_sem))
+ return -EINTR;
if (mm->uprobes_state.xol_area) {
ret = -EALREADY;
goto fail;
@@ -1468,7 +1470,8 @@ static void dup_xol_work(struct callback_head *work)
if (current->flags & PF_EXITING)

- if (!__create_xol_area(current->utask->dup_xol_addr))
+ if (!__create_xol_area(current->utask->dup_xol_addr) &&
+ !fatal_signal_pending(current)
^ missing ")"

Other than that,
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

uprobe_warn(current, "dup xol area");