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Subject[PATCH 01/17] drbd: narrow rcu_read_lock in drbd_sync_handshake
Date
From: Roland Kammerer <roland.kammerer@linbit.com>

So far there was the possibility that we called
genlmsg_new(GFP_NOIO)/mutex_lock() while holding an rcu_read_lock().

This included cases like:

drbd_sync_handshake (acquire the RCU lock)
drbd_asb_recover_1p
drbd_khelper
drbd_bcast_event
genlmsg_new(GFP_NOIO) --> may sleep

drbd_sync_handshake (acquire the RCU lock)
drbd_asb_recover_1p
drbd_khelper
notify_helper
genlmsg_new(GFP_NOIO) --> may sleep

drbd_sync_handshake (acquire the RCU lock)
drbd_asb_recover_1p
drbd_khelper
notify_helper
mutex_lock --> may sleep

While using GFP_ATOMIC whould have been possible in the first two cases,
the real fix is to narrow the rcu_read_lock.

Reported-by: Jia-Ju Bai <baijiaju1990@163.com>
Reviewed-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Roland Kammerer <roland.kammerer@linbit.com>
---
drivers/block/drbd/drbd_receiver.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 61c392752fe4..1b9822f264d2 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -3364,7 +3364,7 @@ static enum drbd_conns drbd_sync_handshake(struct drbd_peer_device *peer_device,
enum drbd_conns rv = C_MASK;
enum drbd_disk_state mydisk;
struct net_conf *nc;
- int hg, rule_nr, rr_conflict, tentative;
+ int hg, rule_nr, rr_conflict, tentative, always_asbp;

mydisk = device->state.disk;
if (mydisk == D_NEGOTIATING)
@@ -3415,8 +3415,12 @@ static enum drbd_conns drbd_sync_handshake(struct drbd_peer_device *peer_device,

rcu_read_lock();
nc = rcu_dereference(peer_device->connection->net_conf);
+ always_asbp = nc->always_asbp;
+ rr_conflict = nc->rr_conflict;
+ tentative = nc->tentative;
+ rcu_read_unlock();

- if (hg == 100 || (hg == -100 && nc->always_asbp)) {
+ if (hg == 100 || (hg == -100 && always_asbp)) {
int pcount = (device->state.role == R_PRIMARY)
+ (peer_role == R_PRIMARY);
int forced = (hg == -100);
@@ -3455,9 +3459,6 @@ static enum drbd_conns drbd_sync_handshake(struct drbd_peer_device *peer_device,
"Sync from %s node\n",
(hg < 0) ? "peer" : "this");
}
- rr_conflict = nc->rr_conflict;
- tentative = nc->tentative;
- rcu_read_unlock();

if (hg == -100) {
/* FIXME this log message is not correct if we end up here
--
2.17.1
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