The patch titled
Subject: ipc/shm: kill the historical/wrong mm->start_stack check
has been added to the -mm tree. Its filename is
ipc-shm-kill-the-historical-wrong-mm-start_stack-check.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipc-shm-kill-the-historical-wrong-mm-start_stack-check.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipc-shm-kill-the-historical-wrong-mm-start_stack-check.patch
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The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: ipc/shm: kill the historical/wrong mm->start_stack check
do_shmat() is the only user of ->start_stack (proc just reports its
value), and this check looks ugly and wrong.
The reason for this check is not clear at all, and it wrongly assumes that
the stack can only grow down.
But the main problem is that in general mm->start_stack has nothing to do
with stack_vma->vm_start. Not only the application can switch to another
stack and even unmap this area, setup_arg_pages() expands the stack
without updating mm->start_stack during exec(). This means that in the
likely case "addr > start_stack - size - PAGE_SIZE * 5" is simply
impossible after find_vma_intersection() == F, or the stack can't grow
anyway because of RLIMIT_STACK.
Many thanks to Hugh for his explanations.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
Cc: Davidlohr Bueso <davidlohr.bueso@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/shm.c | 7 -------
1 file changed, 7 deletions(-)
diff -puN ipc/shm.c~ipc-shm-kill-the-historical-wrong-mm-start_stack-check ipc/shm.c
--- a/ipc/shm.c~ipc-shm-kill-the-historical-wrong-mm-start_stack-check
+++ a/ipc/shm.c
@@ -1172,13 +1172,6 @@ long do_shmat(int shmid, char __user *sh
if (find_vma_intersection(current->mm, addr, addr + size))
goto invalid;
- /*
- * If shm segment goes below stack, make sure there is some
- * space left for the stack to grow (at least 4 pages).
- */
- if (addr < current->mm->start_stack &&
- addr > current->mm->start_stack - size - PAGE_SIZE * 5)
- goto invalid;
}
addr = do_mmap_pgoff(file, addr, size, prot, flags, 0, &populate);
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
prctl-pr_set_mm-introduce-pr_set_mm_map-operation-v4.patch
earlyprintk-re-enable-earlyprintk-calling-early_param.patch
fs-proc-task_mmuc-dont-use-task-mm-in-m_start-and-show_map.patch
fs-proc-task_mmuc-unify-simplify-do_maps_open-and-numa_maps_open.patch
proc-introduce-proc_mem_open.patch
fs-proc-task_mmuc-shift-mm_access-from-m_start-to-proc_maps_open.patch
fs-proc-task_mmuc-shift-mm_access-from-m_start-to-proc_maps_open-checkpatch-fixes.patch
fs-proc-task_mmuc-simplify-the-vma_stop-logic.patch
fs-proc-task_mmuc-simplify-the-vma_stop-logic-checkpatch-fixes.patch
fs-proc-task_mmuc-cleanup-the-tail_vma-horror-in-m_next.patch
fs-proc-task_mmuc-shift-priv-task-=-null-from-m_start-to-m_stop.patch
fs-proc-task_mmuc-kill-the-suboptimal-and-confusing-m-version-logic.patch
fs-proc-task_mmuc-simplify-m_start-to-make-it-readable.patch
fs-proc-task_mmuc-introduce-m_next_vma-helper.patch
fs-proc-task_mmuc-reintroduce-m-version-logic.patch
fs-proc-task_mmuc-update-m-version-in-the-main-loop-in-m_start.patch
fs-proc-task_nommuc-change-maps_open-to-use-__seq_open_private.patch
fs-proc-task_nommuc-shift-mm_access-from-m_start-to-proc_maps_open.patch
fs-proc-task_nommuc-shift-mm_access-from-m_start-to-proc_maps_open-checkpatch-fixes.patch
fs-proc-task_nommuc-dont-use-priv-task-mm.patch
ipc-shm-kill-the-historical-wrong-mm-start_stack-check.patch
linux-next.patch
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