--- /dev/null
+From 69175668f0bad4069ccf3023f009967e7d2b71a7 Mon Sep 17 00:00:00 2001
+From: Sasha Levin <sashal@kernel.org>
+Date: Wed, 3 Jun 2020 16:49:44 +0200
+Subject: net: core: device_rename: Use rwsem instead of a seqcount
+
+From: Ahmed S. Darwish <a.darwish@linutronix.de>
+
+[ Upstream commit 11d6011c2cf29f7c8181ebde6c8bc0c4d83adcd7 ]
+
+Sequence counters write paths are critical sections that must never be
+preempted, and blocking, even for CONFIG_PREEMPTION=n, is not allowed.
+
+Commit 5dbe7c178d3f ("net: fix kernel deadlock with interface rename and
+netdev name retrieval.") handled a deadlock, observed with
+CONFIG_PREEMPTION=n, where the devnet_rename seqcount read side was
+infinitely spinning: it got scheduled after the seqcount write side
+blocked inside its own critical section.
+
+To fix that deadlock, among other issues, the commit added a
+cond_resched() inside the read side section. While this will get the
+non-preemptible kernel eventually unstuck, the seqcount reader is fully
+exhausting its slice just spinning -- until TIF_NEED_RESCHED is set.
+
+The fix is also still broken: if the seqcount reader belongs to a
+real-time scheduling policy, it can spin forever and the kernel will
+livelock.
+
+Disabling preemption over the seqcount write side critical section will
+not work: inside it are a number of GFP_KERNEL allocations and mutex
+locking through the drivers/base/ :: device_rename() call chain.
+
+>From all the above, replace the seqcount with a rwsem.
+
+Fixes: 5dbe7c178d3f (net: fix kernel deadlock with interface rename and netdev name retrieval.)
+Fixes: 30e6c9fa93cf (net: devnet_rename_seq should be a seqcount)
+Fixes: c91f6df2db49 (sockopt: Change getsockopt() of SO_BINDTODEVICE to return an interface name)
+Cc: <stable@vger.kernel.org>
+Reported-by: kbuild test robot <lkp@intel.com> [ v1 missing up_read() on error exit ]
+Reported-by: Dan Carpenter <dan.carpenter@oracle.com> [ v1 missing up_read() on error exit ]
+Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
+Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Signed-off-by: Sasha Levin <sashal@kernel.org>
+---
+ net/core/dev.c | 40 ++++++++++++++++++----------------------
+ 1 file changed, 18 insertions(+), 22 deletions(-)
+
+diff --git a/net/core/dev.c b/net/core/dev.c
+index b127f022d8bd9..204d87e7c9b19 100644
+--- a/net/core/dev.c
++++ b/net/core/dev.c
+@@ -79,6 +79,7 @@
+ #include <linux/sched.h>
+ #include <linux/sched/mm.h>
+ #include <linux/mutex.h>
++#include <linux/rwsem.h>
+ #include <linux/string.h>
+ #include <linux/mm.h>
+ #include <linux/socket.h>
+@@ -194,7 +195,7 @@ static DEFINE_SPINLOCK(napi_hash_lock);
+ static unsigned int napi_gen_id = NR_CPUS;
+ static DEFINE_READ_MOSTLY_HASHTABLE(napi_hash, 8);
+
+-static seqcount_t devnet_rename_seq;
++static DECLARE_RWSEM(devnet_rename_sem);
+
+ static inline void dev_base_seq_inc(struct net *net)
+ {
+@@ -816,33 +817,28 @@ EXPORT_SYMBOL(dev_get_by_napi_id);
+ * @net: network namespace
+ * @name: a pointer to the buffer where the name will be stored.
+ * @ifindex: the ifindex of the interface to get the name from.
+- *
+- * The use of raw_seqcount_begin() and cond_resched() before
+- * retrying is required as we want to give the writers a chance
+- * to complete when CONFIG_PREEMPTION is not set.
+ */
+ int netdev_get_name(struct net *net, char *name, int ifindex)
+ {
+ struct net_device *dev;
+- unsigned int seq;
++ int ret;
+
+-retry:
+- seq = raw_seqcount_begin(&devnet_rename_seq);
++ down_read(&devnet_rename_sem);
+ rcu_read_lock();
++
+ dev = dev_get_by_index_rcu(net, ifindex);
+ if (!dev) {
+- rcu_read_unlock();
+- return -ENODEV;
++ ret = -ENODEV;
++ goto out;
+ }
+
+ strcpy(name, dev->name);
+- rcu_read_unlock();
+- if (read_seqcount_retry(&devnet_rename_seq, seq)) {
+- cond_resched();
+- goto retry;
+- }
+
+- return 0;
++ ret = 0;
++out:
++ rcu_read_unlock();
++ up_read(&devnet_rename_sem);
++ return ret;
+ }
+
+ /**
+@@ -1115,10 +1111,10 @@ int dev_change_name(struct net_device *dev, const char *newname)
+ likely(!(dev->priv_flags & IFF_LIVE_RENAME_OK)))
+ return -EBUSY;
+
+- write_seqcount_begin(&devnet_rename_seq);
++ down_write(&devnet_rename_sem);
+
+ if (strncmp(newname, dev->name, IFNAMSIZ) == 0) {
+- write_seqcount_end(&devnet_rename_seq);
++ up_write(&devnet_rename_sem);
+ return 0;
+ }
+
+@@ -1126,7 +1122,7 @@ int dev_change_name(struct net_device *dev, const char *newname)
+
+ err = dev_get_valid_name(net, dev, newname);
+ if (err < 0) {
+- write_seqcount_end(&devnet_rename_seq);
++ up_write(&devnet_rename_sem);
+ return err;
+ }
+
+@@ -1141,11 +1137,11 @@ rollback:
+ if (ret) {
+ memcpy(dev->name, oldname, IFNAMSIZ);
+ dev->name_assign_type = old_assign_type;
+- write_seqcount_end(&devnet_rename_seq);
++ up_write(&devnet_rename_sem);
+ return ret;
+ }
+
+- write_seqcount_end(&devnet_rename_seq);
++ up_write(&devnet_rename_sem);
+
+ netdev_adjacent_rename_links(dev, oldname);
+
+@@ -1166,7 +1162,7 @@ rollback:
+ /* err >= 0 after dev_alloc_name() or stores the first errno */
+ if (err >= 0) {
+ err = ret;
+- write_seqcount_begin(&devnet_rename_seq);
++ down_write(&devnet_rename_sem);
+ memcpy(dev->name, oldname, IFNAMSIZ);
+ memcpy(oldname, newname, IFNAMSIZ);
+ dev->name_assign_type = old_assign_type;
+--
+2.25.1
+
--- /dev/null
+From 70271c251b13ae20eafb1173b8273e864a60d419 Mon Sep 17 00:00:00 2001
+From: Sasha Levin <sashal@kernel.org>
+Date: Tue, 15 Oct 2019 21:18:08 +0200
+Subject: sched/rt, net: Use CONFIG_PREEMPTION.patch
+
+From: Thomas Gleixner <tglx@linutronix.de>
+
+[ Upstream commit 2da2b32fd9346009e9acdb68c570ca8d3966aba7 ]
+
+CONFIG_PREEMPTION is selected by CONFIG_PREEMPT and by CONFIG_PREEMPT_RT.
+Both PREEMPT and PREEMPT_RT require the same functionality which today
+depends on CONFIG_PREEMPT.
+
+Update the comment to use CONFIG_PREEMPTION.
+
+Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
+Acked-by: David S. Miller <davem@davemloft.net>
+Cc: Linus Torvalds <torvalds@linux-foundation.org>
+Cc: Peter Zijlstra <peterz@infradead.org>
+Cc: netdev@vger.kernel.org
+Link: https://lore.kernel.org/r/20191015191821.11479-22-bigeasy@linutronix.de
+Signed-off-by: Ingo Molnar <mingo@kernel.org>
+Signed-off-by: Sasha Levin <sashal@kernel.org>
+---
+ net/core/dev.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/net/core/dev.c b/net/core/dev.c
+index 8552874e5aac1..b127f022d8bd9 100644
+--- a/net/core/dev.c
++++ b/net/core/dev.c
+@@ -819,7 +819,7 @@ EXPORT_SYMBOL(dev_get_by_napi_id);
+ *
+ * The use of raw_seqcount_begin() and cond_resched() before
+ * retrying is required as we want to give the writers a chance
+- * to complete when CONFIG_PREEMPT is not set.
++ * to complete when CONFIG_PREEMPTION is not set.
+ */
+ int netdev_get_name(struct net *net, char *name, int ifindex)
+ {
+--
+2.25.1
+
projects / thirdparty / kernel / stable-queue.git / commitdiff
