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authorChristoph Hellwig <hch@lst.de>2020-06-10 18:42:10 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-10 19:14:18 -0700
commit37c54f9bd48663f7657a9178fe08c47e4f5b537b (patch)
treeba38e9216da172c16c4beafa97a882fc85f86068 /kernel
parentf5678e7f2ac31c270334b936352f0ef2fe7dd2b3 (diff)
kernel: set USER_DS in kthread_use_mm
Some architectures like arm64 and s390 require USER_DS to be set for kernel threads to access user address space, which is the whole purpose of kthread_use_mm, but other like x86 don't. That has lead to a huge mess where some callers are fixed up once they are tested on said architectures, while others linger around and yet other like io_uring try to do "clever" optimizations for what usually is just a trivial asignment to a member in the thread_struct for most architectures. Make kthread_use_mm set USER_DS, and kthread_unuse_mm restore to the previous value instead. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Jens Axboe <axboe@kernel.dk> Reviewed-by: Jens Axboe <axboe@kernel.dk> Acked-by: Michael S. Tsirkin <mst@redhat.com> Cc: Alex Deucher <alexander.deucher@amd.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Felipe Balbi <balbi@kernel.org> Cc: Felix Kuehling <Felix.Kuehling@amd.com> Cc: Jason Wang <jasowang@redhat.com> Cc: Zhenyu Wang <zhenyuw@linux.intel.com> Cc: Zhi Wang <zhi.a.wang@intel.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Link: http://lkml.kernel.org/r/20200404094101.672954-7-hch@lst.de Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/kthread.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 8ed4b4fbec7c..86357cd38eb2 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -52,6 +52,7 @@ struct kthread {
unsigned long flags;
unsigned int cpu;
void *data;
+ mm_segment_t oldfs;
struct completion parked;
struct completion exited;
#ifdef CONFIG_BLK_CGROUP
@@ -1235,6 +1236,9 @@ void kthread_use_mm(struct mm_struct *mm)
if (active_mm != mm)
mmdrop(active_mm);
+
+ to_kthread(tsk)->oldfs = get_fs();
+ set_fs(USER_DS);
}
EXPORT_SYMBOL_GPL(kthread_use_mm);
@@ -1249,6 +1253,8 @@ void kthread_unuse_mm(struct mm_struct *mm)
WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
WARN_ON_ONCE(!tsk->mm);
+ set_fs(to_kthread(tsk)->oldfs);
+
task_lock(tsk);
sync_mm_rss(mm);
tsk->mm = NULL;