lkml.org 
[lkml]   [2014]   [Jan]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH v2 2/2] change close_files() to use rcu_dereference_raw(files->fdt)
put_files_struct() and close_files() do rcu_read_lock() to make
rcu_dereference_check_fdtable() happy.

This looks a bit ugly, files_fdtable() just reads the pointer,
we can simply use rcu_dereference_raw() to avoid the warning.

The patch also changes close_files() to return fdt, this avoids
another rcu_read_lock()/files_fdtable() in put_files_struct().

I think close_files() needs more cleanups:

- we do not need xchg() exactly because we are the last
user of this files_struct

- "if (file)" should be turned into WARN_ON(!file)

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
fs/file.c | 26 +++++++++-----------------
1 files changed, 9 insertions(+), 17 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index 957cbc0..d34e59e 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -348,21 +348,16 @@ out:
return NULL;
}

-static void close_files(struct files_struct * files)
+static struct fdtable *close_files(struct files_struct * files)
{
- int i, j;
- struct fdtable *fdt;
-
- j = 0;
-
/*
* It is safe to dereference the fd table without RCU or
* ->file_lock because this is the last reference to the
- * files structure. But use RCU to shut RCU-lockdep up.
+ * files structure.
*/
- rcu_read_lock();
- fdt = files_fdtable(files);
- rcu_read_unlock();
+ struct fdtable *fdt = rcu_dereference_raw(files->fdt);
+ int i, j = 0;
+
for (;;) {
unsigned long set;
i = j * BITS_PER_LONG;
@@ -381,6 +376,8 @@ static void close_files(struct files_struct * files)
set >>= 1;
}
}
+
+ return fdt;
}

struct files_struct *get_files_struct(struct task_struct *task)
@@ -398,14 +395,9 @@ struct files_struct *get_files_struct(struct task_struct *task)

void put_files_struct(struct files_struct *files)
{
- struct fdtable *fdt;
-
if (atomic_dec_and_test(&files->count)) {
- close_files(files);
- /* not really needed, since nobody can see us */
- rcu_read_lock();
- fdt = files_fdtable(files);
- rcu_read_unlock();
+ struct fdtable *fdt = close_files(files);
+
/* free the arrays if they are not embedded */
if (fdt != &files->fdtab)
__free_fdtable(fdt);
--
1.5.5.1



\
 
 \ /
  Last update: 2014-01-11 20:01    [W:0.127 / U:0.244 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site