Re: [PATCH v2][AX25] af_ax25: remove sock lock in ax25_info_show()

[David Miller]

From: Jarek Poplawski [EMAIL PROTECTED]
Date: Sun, 10 Feb 2008 14:10:51 +0100

 [AX25] af_ax25: remove sock lock in ax25_info_show()
  
 This lockdep warning:
 
  ===
  [ INFO: possible circular locking dependency detected ]
  2.6.24 #3
  ---
  swapper/0 is trying to acquire lock:
   (ax25_list_lock){-+..}, at: [f91dd3b1] ax25_destroy_socket+0x171/0x1f0 
  [ax25]
  
  but task is already holding lock:
   (slock-AF_AX25){-+..}, at: [f91dbabc] 
  ax25_std_heartbeat_expiry+0x1c/0xe0 [ax25]
  
  which lock already depends on the new lock.
 ...
 
 shows that ax25_list_lock and slock-AF_AX25 are taken in different
 order: ax25_info_show() takes slock (bh_lock_sock(ax25-sk)) while
 ax25_list_lock is held, so reversely to other functions. To fix this
 the sock lock should be moved to ax25_info_start(), and there would
 be still problem with breaking ax25_list_lock (it seems this proper
 order isn't optimal yet). But, since it's only for reading proc info
 it seems this is not necessary (e.g.  ax25_send_to_raw() does similar
 reading without this lock too).
 
 So, this patch removes sock lock to avoid deadlock possibility; there
 is also used sock_i_ino() function, which reads sk_socket under proper
 read lock. Additionally printf format of this i_ino is changed to %lu.
 
 Reported-by: Bernard Pidoux F6BVP [EMAIL PROTECTED]
 Signed-off-by: Jarek Poplawski [EMAIL PROTECTED]

Applied, thanks Jarek.

 +sock_i_ino(ax25-sk));

Note that this taks the sk callback lock, it should be OK but
let's keep a watch out for any new lockdep warnings this
ends up causing :-)
--
To unsubscribe from this list: send the line unsubscribe netdev in
the body of a message to [EMAIL PROTECTED]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[PATCH v2][AX25] af_ax25: remove sock lock in ax25_info_show()

[Jarek Poplawski]

Hi,

Here is a little bit better version, I hope.

Regards,
Jarek P.

-- (take 2)

Subject: [AX25] af_ax25: remove sock lock in ax25_info_show()
 
This lockdep warning:

 ===
 [ INFO: possible circular locking dependency detected ]
 2.6.24 #3
 ---
 swapper/0 is trying to acquire lock:
  (ax25_list_lock){-+..}, at: [f91dd3b1] ax25_destroy_socket+0x171/0x1f0 
 [ax25]
 
 but task is already holding lock:
  (slock-AF_AX25){-+..}, at: [f91dbabc] ax25_std_heartbeat_expiry+0x1c/0xe0 
 [ax25]
 
 which lock already depends on the new lock.
...

shows that ax25_list_lock and slock-AF_AX25 are taken in different
order: ax25_info_show() takes slock (bh_lock_sock(ax25-sk)) while
ax25_list_lock is held, so reversely to other functions. To fix this
the sock lock should be moved to ax25_info_start(), and there would
be still problem with breaking ax25_list_lock (it seems this proper
order isn't optimal yet). But, since it's only for reading proc info
it seems this is not necessary (e.g.  ax25_send_to_raw() does similar
reading without this lock too).

So, this patch removes sock lock to avoid deadlock possibility; there
is also used sock_i_ino() function, which reads sk_socket under proper
read lock. Additionally printf format of this i_ino is changed to %lu.


Reported-by: Bernard Pidoux F6BVP [EMAIL PROTECTED]
Signed-off-by: Jarek Poplawski [EMAIL PROTECTED]

---

 net/ax25/af_ax25.c |6 ++
 1 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 94b2b1b..48bfcc7 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1924,12 +1924,10 @@ static int ax25_info_show(struct seq_file *seq, void *v)
   ax25-paclen);
 
if (ax25-sk != NULL) {
-   bh_lock_sock(ax25-sk);
-   seq_printf(seq, %d %d %ld\n,
+   seq_printf(seq,  %d %d %lu\n,
   atomic_read(ax25-sk-sk_wmem_alloc),
   atomic_read(ax25-sk-sk_rmem_alloc),
-  ax25-sk-sk_socket != NULL ? 
SOCK_INODE(ax25-sk-sk_socket)-i_ino : 0L);
-   bh_unlock_sock(ax25-sk);
+  sock_i_ino(ax25-sk));
} else {
seq_puts(seq,  * * *\n);
}
--
To unsubscribe from this list: send the line unsubscribe netdev in
the body of a message to [EMAIL PROTECTED]
More majordomo info at  http://vger.kernel.org/majordomo-info.html