pm24.git/kernel/rcu/tree_plugin.h, branch v5.6

Merge branches 'doc.2019.12.10a', 'exp.2019.12.09a', 'fixes.2020.01.24a', 'kfree_rcu.2020.01.24a', 'list.2020.01.10a', 'preempt.2020.01.24a' and 'torture.2019.12.09a' into HEAD

2020-01-24T18:37:27Z

doc.2019.12.10a: Documentations updates exp.2019.12.09a: Expedited grace-period updates fixes.2020.01.24a: Miscellaneous fixes kfree_rcu.2020.01.24a: Batch kfree_rcu() work list.2020.01.10a: RCU-protected-list updates preempt.2020.01.24a: Preemptible RCU updates torture.2019.12.09a: Torture-test updates

rcu: Provide wrappers for uses of ->rcu_read_lock_nesting

2020-01-24T18:27:33Z

This commit provides wrapper functions for uses of ->rcu_read_lock_nesting to improve readability and to ease future changes to support inlining of __rcu_read_lock() and __rcu_read_unlock(). Signed-off-by: Lai Jiangshan Signed-off-by: Paul E. McKenney

rcu: Use READ_ONCE() for ->expmask in rcu_read_unlock_special()

2020-01-24T18:27:33Z

The rcu_node structure's ->expmask field is updated only when holding the ->lock, but is also accessed locklessly. This means that all ->expmask updates must use WRITE_ONCE() and all reads carried out without holding ->lock must use READ_ONCE(). This commit therefore changes the lockless ->expmask read in rcu_read_unlock_special() to use READ_ONCE(). Reported-by: syzbot+99f4ddade3c22ab0cf23@syzkaller.appspotmail.com Signed-off-by: Paul E. McKenney Acked-by: Marco Elver

rcu: Clear ->rcu_read_unlock_special only once

2020-01-24T18:27:33Z

In rcu_preempt_deferred_qs_irqrestore(), ->rcu_read_unlock_special is cleared one piece at a time. Given that the "if" statements in this function use the copy in "special", this commit removes the clearing of the individual pieces in favor of clearing ->rcu_read_unlock_special in one go just after it has been determined to be non-zero. Signed-off-by: Lai Jiangshan Signed-off-by: Paul E. McKenney

rcu: Clear .exp_hint only when deferred quiescent state has been reported

2020-01-24T18:27:33Z

Currently, the .exp_hint flag is cleared in rcu_read_unlock_special(), which works, but which can also prevent subsequent rcu_read_unlock() calls from helping expedite the quiescent state needed by an ongoing expedited RCU grace period. This commit therefore defers clearing of .exp_hint from rcu_read_unlock_special() to rcu_preempt_deferred_qs_irqrestore(), thus ensuring that intervening calls to rcu_read_unlock() have a chance to help end the expedited grace period. Signed-off-by: Lai Jiangshan Signed-off-by: Paul E. McKenney

rcu: Remove kfree_rcu() special casing and lazy-callback handling

2020-01-24T18:24:31Z

This commit removes kfree_rcu() special-casing and the lazy-callback handling from Tree RCU. It moves some of this special casing to Tiny RCU, the removal of which will be the subject of later commits. This results in a nice negative delta. Suggested-by: Paul E. McKenney Signed-off-by: Joel Fernandes (Google) [ paulmck: Add slab.h #include, thanks to kbuild test robot . ] Signed-off-by: Paul E. McKenney

rcu: Use CONFIG_PREEMPTION where appropriate

2019-12-09T20:37:51Z

The config option `CONFIG_PREEMPT' is used for the preemption model "Low-Latency Desktop". The config option `CONFIG_PREEMPTION' is enabled when kernel preemption is enabled which is true for the preemption model `CONFIG_PREEMPT' and `CONFIG_PREEMPT_RT'. Use `CONFIG_PREEMPTION' if it applies to both preemption models and not just to `CONFIG_PREEMPT'. Cc: "Paul E. McKenney" Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Cc: Joel Fernandes Cc: Davidlohr Bueso Cc: rcu@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Paul E. McKenney

rcu: Use lockdep rather than comment to enforce lock held

2019-12-09T20:37:50Z

The rcu_preempt_check_blocked_tasks() function has a comment that states that the rcu_node structure's ->lock must be held, which might be informative, but which carries little weight if not read. This commit therefore removes this comment in favor of raw_lockdep_assert_held_rcu_node(), which will complain quite visibly if the required lock is not held. Signed-off-by: Paul E. McKenney

rcu: Avoid data-race in rcu_gp_fqs_check_wake()

2019-12-09T20:37:50Z

The rcu_gp_fqs_check_wake() function uses rcu_preempt_blocked_readers_cgp() to read ->gp_tasks while other cpus might overwrite this field. We need READ_ONCE()/WRITE_ONCE() pairs to avoid compiler tricks and KCSAN splats like the following : BUG: KCSAN: data-race in rcu_gp_fqs_check_wake / rcu_preempt_deferred_qs_irqrestore write to 0xffffffff85a7f190 of 8 bytes by task 7317 on cpu 0: rcu_preempt_deferred_qs_irqrestore+0x43d/0x580 kernel/rcu/tree_plugin.h:507 rcu_read_unlock_special+0xec/0x370 kernel/rcu/tree_plugin.h:659 __rcu_read_unlock+0xcf/0xe0 kernel/rcu/tree_plugin.h:394 rcu_read_unlock include/linux/rcupdate.h:645 [inline] __ip_queue_xmit+0x3b0/0xa40 net/ipv4/ip_output.c:533 ip_queue_xmit+0x45/0x60 include/net/ip.h:236 __tcp_transmit_skb+0xdeb/0x1cd0 net/ipv4/tcp_output.c:1158 __tcp_send_ack+0x246/0x300 net/ipv4/tcp_output.c:3685 tcp_send_ack+0x34/0x40 net/ipv4/tcp_output.c:3691 tcp_cleanup_rbuf+0x130/0x360 net/ipv4/tcp.c:1575 tcp_recvmsg+0x633/0x1a30 net/ipv4/tcp.c:2179 inet_recvmsg+0xbb/0x250 net/ipv4/af_inet.c:838 sock_recvmsg_nosec net/socket.c:871 [inline] sock_recvmsg net/socket.c:889 [inline] sock_recvmsg+0x92/0xb0 net/socket.c:885 sock_read_iter+0x15f/0x1e0 net/socket.c:967 call_read_iter include/linux/fs.h:1864 [inline] new_sync_read+0x389/0x4f0 fs/read_write.c:414 read to 0xffffffff85a7f190 of 8 bytes by task 10 on cpu 1: rcu_gp_fqs_check_wake kernel/rcu/tree.c:1556 [inline] rcu_gp_fqs_check_wake+0x93/0xd0 kernel/rcu/tree.c:1546 rcu_gp_fqs_loop+0x36c/0x580 kernel/rcu/tree.c:1611 rcu_gp_kthread+0x143/0x220 kernel/rcu/tree.c:1768 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352 Reported by Kernel Concurrency Sanitizer on: CPU: 1 PID: 10 Comm: rcu_preempt Not tainted 5.3.0+ #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Signed-off-by: Eric Dumazet Reported-by: syzbot [ paulmck: Added another READ_ONCE() for RCU CPU stall warnings. ] Signed-off-by: Paul E. McKenney

rcu/nocb: Fix dump_tree hierarchy print always active

2019-12-09T20:37:50Z

Commit 18cd8c93e69e ("rcu/nocb: Print gp/cb kthread hierarchy if dump_tree") added print statements to rcu_organize_nocb_kthreads for debugging, but incorrectly guarded them, causing the function to always spew out its message. This patch fixes it by guarding both pr_alert statements with dump_tree, while also changing the second pr_alert to a pr_cont, to print the hierarchy in a single line (assuming that's how it was supposed to work). Fixes: 18cd8c93e69e ("rcu/nocb: Print gp/cb kthread hierarchy if dump_tree") Signed-off-by: Stefan Reiter [ paulmck: Make single-nocbs-CPU GP kthreads look less erroneous. ] Signed-off-by: Paul E. McKenney