* [PATCH] fget: Do not loop with rcu lock held
@ 2020-12-15 16:41 Sergey Temerkhanov
2020-12-15 17:13 ` Matthew Wilcox
2020-12-16 2:47 ` Al Viro
0 siblings, 2 replies; 3+ messages in thread
From: Sergey Temerkhanov @ 2020-12-15 16:41 UTC (permalink / raw)
To: Alexander Viro, linux-fsdevel, linux-kernel; +Cc: Sergey Temerkhanov
Unlock RCU before running another loop iteration
Signed-off-by: Sergey Temerkhanov <s.temerkhanov@gmail.com>
---
fs/file.c | 34 ++++++++++++++++++++--------------
1 file changed, 20 insertions(+), 14 deletions(-)
diff --git a/fs/file.c b/fs/file.c
index 4559b5fec3bd..49d57752e7a6 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -823,21 +823,27 @@ static struct file *__fget_files(struct files_struct *files, unsigned int fd,
fmode_t mask, unsigned int refs)
{
struct file *file;
+ bool again = false;
- rcu_read_lock();
-loop:
- file = fcheck_files(files, fd);
- if (file) {
- /* File object ref couldn't be taken.
- * dup2() atomicity guarantee is the reason
- * we loop to catch the new file (or NULL pointer)
- */
- if (file->f_mode & mask)
- file = NULL;
- else if (!get_file_rcu_many(file, refs))
- goto loop;
- }
- rcu_read_unlock();
+ do {
+ rcu_read_lock();
+
+ file = fcheck_files(files, fd);
+ if (file) {
+ /* File object ref couldn't be taken.
+ * dup2() atomicity guarantee is the reason
+ * we loop to catch the new file (or NULL pointer)
+ */
+ if (file->f_mode & mask)
+ file = NULL;
+ else if (!get_file_rcu_many(file, refs))
+ again = true;
+ }
+ rcu_read_unlock();
+
+ if (unlikely(again))
+ schedule();
+ } while (again);
return file;
}
--
2.25.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] fget: Do not loop with rcu lock held
2020-12-15 16:41 [PATCH] fget: Do not loop with rcu lock held Sergey Temerkhanov
@ 2020-12-15 17:13 ` Matthew Wilcox
2020-12-16 2:47 ` Al Viro
1 sibling, 0 replies; 3+ messages in thread
From: Matthew Wilcox @ 2020-12-15 17:13 UTC (permalink / raw)
To: Sergey Temerkhanov; +Cc: Alexander Viro, linux-fsdevel, linux-kernel
On Tue, Dec 15, 2020 at 07:41:23PM +0300, Sergey Temerkhanov wrote:
> Unlock RCU before running another loop iteration
Why?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] fget: Do not loop with rcu lock held
2020-12-15 16:41 [PATCH] fget: Do not loop with rcu lock held Sergey Temerkhanov
2020-12-15 17:13 ` Matthew Wilcox
@ 2020-12-16 2:47 ` Al Viro
1 sibling, 0 replies; 3+ messages in thread
From: Al Viro @ 2020-12-16 2:47 UTC (permalink / raw)
To: Sergey Temerkhanov; +Cc: linux-fsdevel, linux-kernel
On Tue, Dec 15, 2020 at 07:41:23PM +0300, Sergey Temerkhanov wrote:
> Unlock RCU before running another loop iteration
If you are able to keep it looping for a long time, I would really
like to see the reproducer.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-12-16 2:48 UTC | newest]
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2020-12-15 16:41 [PATCH] fget: Do not loop with rcu lock held Sergey Temerkhanov
2020-12-15 17:13 ` Matthew Wilcox
2020-12-16 2:47 ` Al Viro
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