The patch titled
Subject: mm: reduce the rcu lock duration
has been added to the -mm mm-unstable branch. Its filename is
mm-reduce-the-rcu-lock-duration.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-reduce-the-rcu-lock-duration.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Subject: mm: reduce the rcu lock duration
Date: Mon, 30 May 2022 19:30:13 +0800
Patch series "A few cleanup and fixup patches for migration", v4.
This series contains a few patches to remove unneeded lock page and
PageMovable check, reduce the rcu lock duration. Also we fix potential
pte_unmap on an not mapped pte. More details can be found in the
respective changelogs.
This patch (of 4):
Commit 3268c63eded4 ("mm: fix move/migrate_pages() race on task struct")
extends the period of the rcu_read_lock until after the permissions checks
are done to prevent the task pointed to from changing from under us. But
the task_struct refcount is also taken at that time, the reference to task
is guaranteed to be stable. So it's unnecessary to extend the period of
the rcu_read_lock. Release the rcu lock after task refcount is
successfully grabbed to reduce the rcu holding time.
Link: https://lkml.kernel.org/r/20220530113016.16663-1-linmiaohe@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20220530113016.16663-2-linmiaohe@xxxxxxxxxx
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mempolicy.c | 3 +--
mm/migrate.c | 3 +--
2 files changed, 2 insertions(+), 4 deletions(-)
--- a/mm/mempolicy.c~mm-reduce-the-rcu-lock-duration
+++ a/mm/mempolicy.c
@@ -1609,6 +1609,7 @@ static int kernel_migrate_pages(pid_t pi
goto out;
}
get_task_struct(task);
+ rcu_read_unlock();
err = -EINVAL;
@@ -1617,11 +1618,9 @@ static int kernel_migrate_pages(pid_t pi
* Use the regular "ptrace_may_access()" checks.
*/
if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
- rcu_read_unlock();
err = -EPERM;
goto out_put;
}
- rcu_read_unlock();
task_nodes = cpuset_mems_allowed(task);
/* Is the user allowed to access the target nodes? */
--- a/mm/migrate.c~mm-reduce-the-rcu-lock-duration
+++ a/mm/migrate.c
@@ -1902,17 +1902,16 @@ static struct mm_struct *find_mm_struct(
return ERR_PTR(-ESRCH);
}
get_task_struct(task);
+ rcu_read_unlock();
/*
* Check if this process has the right to modify the specified
* process. Use the regular "ptrace_may_access()" checks.
*/
if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
- rcu_read_unlock();
mm = ERR_PTR(-EPERM);
goto out;
}
- rcu_read_unlock();
mm = ERR_PTR(security_task_movememory(task));
if (IS_ERR(mm))
_
Patches currently in -mm which might be from linmiaohe@xxxxxxxxxx are
maintainers-add-maintainer-information-for-z3fold.patch
mm-shmemc-clean-up-comment-of-shmem_swapin_folio.patch
mm-reduce-the-rcu-lock-duration.patch
mm-migration-remove-unneeded-lock-page-and-pagemovable-check.patch
mm-migration-return-errno-when-isolate_huge_page-failed.patch
mm-migration-fix-potential-pte_unmap-on-an-not-mapped-pte.patch
