[PATCH 4.13 006/109] srcu: Provide ordering for CPU not involved in grace period

From	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Newsgroups	linux.kernel
Subject	[PATCH 4.13 006/109] srcu: Provide ordering for CPU not involved in grace period
Date	2017-09-24 23:10 +0200
Message-ID	<utmk4-5jg-87@gated-at.bofh.it> (permalink)
References	<utm0F-4Xd-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

commit 35732cf9dd38b1efb0f2f22c91c61b51337d1ac3 upstream.

Tree RCU guarantees that every online CPU has a memory barrier between
any given grace period and any of that CPU's RCU read-side sections that
must be ordered against that grace period.  Since RCU doesn't always
know where read-side critical sections are, the actual implementation
guarantees order against prior and subsequent non-idle non-offline code,
whether in an RCU read-side critical section or not.  As a result, there
does not need to be a memory barrier at the end of synchronize_rcu()
and friends because the ordering internal to the grace period has
ordered every CPU's post-grace-period execution against each CPU's
pre-grace-period execution, again for all non-idle online CPUs.

In contrast, SRCU can have non-idle online CPUs that are completely
uninvolved in a given SRCU grace period, for example, a CPU that
never runs any SRCU read-side critical sections and took no part in
the grace-period processing.  It is in theory possible for a given
synchronize_srcu()'s wakeup to be delivered to a CPU that was completely
uninvolved in the prior SRCU grace period, which could mean that the
code following that synchronize_srcu() would end up being unordered with
respect to both the grace period and any pre-existing SRCU read-side
critical sections.

This commit therefore adds an smp_mb() to the end of __synchronize_srcu(),
which prevents this scenario from occurring.

Reported-by: Lance Roy <ldr709@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Lance Roy <ldr709@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/rcu/srcutree.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -896,6 +896,15 @@ static void __synchronize_srcu(struct sr
 	__call_srcu(sp, &rcu.head, wakeme_after_rcu, do_norm);
 	wait_for_completion(&rcu.completion);
 	destroy_rcu_head_on_stack(&rcu.head);
+
+	/*
+	 * Make sure that later code is ordered after the SRCU grace
+	 * period.  This pairs with the raw_spin_lock_irq_rcu_node()
+	 * in srcu_invoke_callbacks().  Unlike Tree RCU, this is needed
+	 * because the current CPU might have been totally uninvolved with
+	 * (and thus unordered against) that grace period.
+	 */
+	smp_mb();
 }
 
 /**

Thread

[PATCH 4.13 000/109] 4.13.4-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 058/109] scsi: qedi: off by one in qedi_get_cmd_from_tid() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 041/109] powerpc/powernv/npu: Move tlb flush before launching ATSD Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 088/109] media: venus: fix copy/paste error in return_buf_error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 066/109] scsi: sg: fixup infoleak when using SG_GET_REQUEST_TABLE Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 031/109] crypto: scompress - dont sleep with preemption disabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 060/109] scsi: megaraid_sas: mismatch of allocated MFI frame size and length exposed in MFI MPT pass through command Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 039/109] ext4: fix quota inconsistency during orphan cleanup for read-only mounts Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 067/109] scsi: qla2xxx: Update fw_started flags at qpair creation. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 054/109] scsi: zfcp: fix missing trace records for early returns in TMF eh handlers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 083/109] net/netfilter/nf_conntrack_core: Fix net_conntrack_lock() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 028/109] MIPS: math-emu: <MADDF|MSUBF>.D: Fix accuracy (64-bit case) Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 049/109] skd: Submit requests to firmware before triggering the doorbell Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 085/109] s390/mm: fix race on mm->context.flush_mm Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 062/109] scsi: megaraid_sas: Check valid aen class range to avoid kernel panic Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 036/109] wcn36xx: Introduce mutual exclusion of fw configuration Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 037/109] ext4: in ext4_seek_{hole,data}, return -ENXIO for negative offsets Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 078/109] tracing: Fix clear of RECORDED_TGID flag when disabling trace event Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 051/109] scsi: zfcp: add handling for FCP_RESID_OVER to the fcp ingress path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 059/109] scsi: aacraid: Fix command send race condition Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 027/109] MIPS: math-emu: <MADDF|MSUBF>.S: Fix accuracy (32-bit case) Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 052/109] scsi: zfcp: fix capping of unsuccessful GPN_FT SAN response trace records Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 079/109] tracing: Apply trace_clock changes to instance max buffer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 055/109] scsi: zfcp: fix payload with full FCP_RSP IU in SCSI trace records Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 026/109] MIPS: math-emu: <MADDF|MSUBF>.<D|S>: Clean up "maddf_flags" enumeration Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 029/109] docs: disable KASLR when debugging kernel Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 043/109] powerpc: Fix DAR reporting when alignment handler faults Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 046/109] md/bitmap: copy correct data for bitmap super Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 075/109] ftrace: Fix selftest goto location on error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 081/109] PCI: shpchp: Enable bridge bus mastering if MSI is enabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:00 +0200
  [PATCH 4.13 018/109] MIPS: math-emu: <MAX|MAXA|MIN|MINA>.<D|S>: Fix cases of both inputs zero Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 024/109] MIPS: math-emu: <MADDF|MSUBF>.<D|S>: Fix some cases of infinite inputs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 016/109] Input: i8042 - add Gigabyte P57 to the keyboard reset table Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 008/109] Input: xpad - validate USB endpoint type during probe Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 020/109] MIPS: math-emu: <MAXA|MINA>.<D|S>: Fix cases of input values with opposite signs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 023/109] MIPS: math-emu: <MADDF|MSUBF>.<D|S>: Fix NaN propagation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 009/109] drm/amdgpu: read reg in each iterator of psp_wait_for loop Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 010/109] tty: improve tty_insert_flip_char() fast path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 014/109] pinctrl: samsung: Fix NULL pointer exception on external interrupts on S3C24xx Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 022/109] MIPS: math-emu: MINA.<D|S>: Fix some cases of infinity and zero inputs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 011/109] tty: improve tty_insert_flip_char() slow path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 019/109] MIPS: math-emu: <MAX|MIN>.<D|S>: Fix cases of both inputs negative Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 001/109] orangefs: Dont clear SGID when inheriting ACLs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
    Re: [PATCH 4.13 001/109] orangefs: Dont clear SGID when inheriting ACLs Mike Marshall <hubcap@omnibond.com> - 2017-09-26 02:10 +0200
  [PATCH 4.13 004/109] IB/{qib, hfi1}: Avoid flow control testing for RDMA write operation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 006/109] srcu: Provide ordering for CPU not involved in grace period Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  [PATCH 4.13 017/109] MIPS: math-emu: <MAX|MAXA|MIN|MINA>.<D|S>: Fix quiet NaN propagation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:10 +0200
  Re: [PATCH 4.13 000/109] 4.13.4-stable review Guenter Roeck <linux@roeck-us.net> - 2017-09-25 03:10 +0200
    Re: [PATCH 4.13 000/109] 4.13.4-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-25 08:40 +0200
  Re: [PATCH 4.13 000/109] 4.13.4-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-09-26 01:20 +0200
    Re: [PATCH 4.13 000/109] 4.13.4-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-26 09:40 +0200

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