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Eric Dumazet 74e1493e00 net/x25: do not hold the cpu too long in x25_new_lci() commit `cf657d22ee` upstream. Due to quadratic behavior of x25_new_lci(), syzbot was able to trigger an rcu stall. Fix this by not blocking BH for the whole duration of the function, and inserting a reschedule point when possible. If we care enough, using a bitmap could get rid of the quadratic behavior. syzbot report : rcu: INFO: rcu_preempt self-detected stall on CPU rcu: 0-...!: (10500 ticks this GP) idle=4fa/1/0x4000000000000002 softirq=283376/283376 fqs=0 rcu: (t=10501 jiffies g=383105 q=136) rcu: rcu_preempt kthread starved for 10502 jiffies! g383105 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0 rcu: RCU grace-period kthread stack dump: rcu_preempt I28928 10 2 0x80000000 Call Trace: context_switch kernel/sched/core.c:2844 [inline] __schedule+0x817/0x1cc0 kernel/sched/core.c:3485 schedule+0x92/0x180 kernel/sched/core.c:3529 schedule_timeout+0x4db/0xfd0 kernel/time/timer.c:1803 rcu_gp_fqs_loop kernel/rcu/tree.c:1948 [inline] rcu_gp_kthread+0x956/0x17a0 kernel/rcu/tree.c:2105 kthread+0x357/0x430 kernel/kthread.c:246 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352 NMI backtrace for cpu 0 CPU: 0 PID: 8759 Comm: syz-executor2 Not tainted 5.0.0-rc4+ #51 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: <IRQ> __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x172/0x1f0 lib/dump_stack.c:113 nmi_cpu_backtrace.cold+0x63/0xa4 lib/nmi_backtrace.c:101 nmi_trigger_cpumask_backtrace+0x1be/0x236 lib/nmi_backtrace.c:62 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline] rcu_dump_cpu_stacks+0x183/0x1cf kernel/rcu/tree.c:1211 print_cpu_stall kernel/rcu/tree.c:1348 [inline] check_cpu_stall kernel/rcu/tree.c:1422 [inline] rcu_pending kernel/rcu/tree.c:3018 [inline] rcu_check_callbacks.cold+0x500/0xa4a kernel/rcu/tree.c:2521 update_process_times+0x32/0x80 kernel/time/timer.c:1635 tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:161 tick_sched_timer+0x47/0x130 kernel/time/tick-sched.c:1271 __run_hrtimer kernel/time/hrtimer.c:1389 [inline] __hrtimer_run_queues+0x33e/0xde0 kernel/time/hrtimer.c:1451 hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1509 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1035 [inline] smp_apic_timer_interrupt+0x120/0x570 arch/x86/kernel/apic/apic.c:1060 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:807 </IRQ> RIP: 0010:__read_once_size include/linux/compiler.h:193 [inline] RIP: 0010:queued_write_lock_slowpath+0x13e/0x290 kernel/locking/qrwlock.c:86 Code: 00 00 fc ff df 4c 8d 2c 01 41 83 c7 03 41 0f b6 45 00 41 38 c7 7c 08 84 c0 0f 85 0c 01 00 00 8b 03 3d 00 01 00 00 74 1a f3 90 <41> 0f b6 55 00 41 38 d7 7c eb 84 d2 74 e7 48 89 df e8 6c 0f 4f 00 RSP: 0018:ffff88805f117bd8 EFLAGS: 00000206 ORIG_RAX: ffffffffffffff13 RAX: 0000000000000300 RBX: ffffffff89413ba0 RCX: 1ffffffff1282774 RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffffffff89413ba0 RBP: ffff88805f117c70 R08: 1ffffffff1282774 R09: fffffbfff1282775 R10: fffffbfff1282774 R11: ffffffff89413ba3 R12: 00000000000000ff R13: fffffbfff1282774 R14: 1ffff1100be22f7d R15: 0000000000000003 queued_write_lock include/asm-generic/qrwlock.h:104 [inline] do_raw_write_lock+0x1d6/0x290 kernel/locking/spinlock_debug.c:203 __raw_write_lock_bh include/linux/rwlock_api_smp.h:204 [inline] _raw_write_lock_bh+0x3b/0x50 kernel/locking/spinlock.c:312 x25_insert_socket+0x21/0xe0 net/x25/af_x25.c:267 x25_bind+0x273/0x340 net/x25/af_x25.c:705 __sys_bind+0x23f/0x290 net/socket.c:1505 __do_sys_bind net/socket.c:1516 [inline] __se_sys_bind net/socket.c:1514 [inline] __x64_sys_bind+0x73/0xb0 net/socket.c:1514 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x457e39 Code: ad b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007fafccd0dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000031 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457e39 RDX: 0000000000000012 RSI: 0000000020000240 RDI: 0000000000000004 RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007fafccd0e6d4 R13: 00000000004bdf8b R14: 00000000004ce4b8 R15: 00000000ffffffff Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 CPU: 1 PID: 8752 Comm: syz-executor4 Not tainted 5.0.0-rc4+ #51 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:__x25_find_socket+0x78/0x120 net/x25/af_x25.c:328 Code: 89 f8 48 c1 e8 03 80 3c 18 00 0f 85 a6 00 00 00 4d 8b 64 24 68 4d 85 e4 74 7f e8 03 97 3d fb 49 83 ec 68 74 74 e8 f8 96 3d fb <49> 8d bc 24 88 04 00 00 48 89 f8 48 c1 e8 03 0f b6 04 18 84 c0 74 RSP: 0018:ffff8880639efc58 EFLAGS: 00000246 RAX: 0000000000040000 RBX: dffffc0000000000 RCX: ffffc9000e677000 RDX: 0000000000040000 RSI: ffffffff863244b8 RDI: ffff88806a764628 RBP: ffff8880639efc80 R08: ffff8880a80d05c0 R09: fffffbfff1282775 R10: fffffbfff1282774 R11: ffffffff89413ba3 R12: ffff88806a7645c0 R13: 0000000000000001 R14: ffff88809f29ac00 R15: 0000000000000000 FS: 00007fe8d0c58700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000001b32823000 CR3: 00000000672eb000 CR4: 00000000001406e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: x25_new_lci net/x25/af_x25.c:357 [inline] x25_connect+0x374/0xdf0 net/x25/af_x25.c:786 __sys_connect+0x266/0x330 net/socket.c:1686 __do_sys_connect net/socket.c:1697 [inline] __se_sys_connect net/socket.c:1694 [inline] __x64_sys_connect+0x73/0xb0 net/socket.c:1694 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x457e39 Code: ad b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007fe8d0c57c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457e39 RDX: 0000000000000012 RSI: 0000000020000200 RDI: 0000000000000004 RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007fe8d0c586d4 R13: 00000000004be378 R14: 00000000004ceb00 R15: 00000000ffffffff Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot <syzkaller@googlegroups.com> Cc: Andrew Hendry <andrew.hendry@gmail.com> Cc: linux-x25@vger.kernel.org Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2019-02-23 09:07:27 +01:00
arch	x86/a.out: Clear the dump structure initially	2019-02-20 10:25:49 +01:00
block	blk-mq: fix a hung issue when fsync	2019-02-20 10:25:36 +01:00
certs	export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR()	2018-08-22 23:21:44 +09:00
crypto	net: crypto set sk to NULL when af_alg_release.	2019-02-23 09:07:24 +01:00
Documentation	dt-bindings: eeprom: at24: add "atmel,24c2048" compatible string	2019-02-20 10:25:35 +01:00
drivers	PCI: Fix __initdata issue with "pci=disable_acs_redir" parameter	2019-02-23 09:07:26 +01:00
firmware	kbuild: remove all dummy assignments to obj-	2017-11-18 11:46:06 +09:00
fs	mm: proc: smaps_rollup: fix pss_locked calculation	2019-02-20 10:25:50 +01:00
include	net: Add header for usage of fls64()	2019-02-23 09:07:25 +01:00
init	kbuild: Disable LD_DEAD_CODE_DATA_ELIMINATION with ftrace & GCC <= 4.7	2019-01-22 21:40:34 +01:00
ipc	ipc/shm.c: use ERR_CAST() for shm_lock() error return	2018-10-05 16:32:04 -07:00
kernel	signal: Restore the stop PTRACE_EVENT_EXIT	2019-02-20 10:25:48 +01:00
lib	lib/test_rhashtable: Make test_insert_dup() allocate its hash table dynamically	2019-02-12 19:47:21 +01:00
LICENSES	LICENSES: Remove CC-BY-SA-4.0 license text	2018-10-18 11:28:50 +02:00
mm	Revert "mm: slowly shrink slabs with a relatively small number of objects"	2019-02-20 10:25:47 +01:00
net	net/x25: do not hold the cpu too long in x25_new_lci()	2019-02-23 09:07:27 +01:00
samples	samples: mei: use /dev/mei0 instead of /dev/mei	2019-02-15 08:10:11 +01:00
scripts	scripts/gdb: fix lx-version string output	2019-02-12 19:47:20 +01:00
security	smack: fix access permissions for keyring	2019-02-12 19:47:05 +01:00
sound	ASoC: hdmi-codec: fix oops on re-probe	2019-02-20 10:25:45 +01:00
tools	tools uapi: fix Alpha support	2019-02-20 10:25:45 +01:00
usr	initramfs: move gen_initramfs_list.sh from scripts/ to usr/	2018-08-22 23:21:44 +09:00
virt	kvm: fix kvm_ioctl_create_device() reference counting (CVE-2019-6974)	2019-02-12 19:47:25 +01:00
.clang-format	clang-format: Set IndentWrappedFunctionNames false	2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes	.gitattributes: set git diff driver for C source code files	2016-10-07 18:46:30 -07:00
.gitignore	Kbuild updates for v4.17 (2nd)	2018-04-15 17:21:30 -07:00
.mailmap	libnvdimm-for-4.19_misc	2018-08-25 18:13:10 -07:00
COPYING	COPYING: use the new text with points to the license files	2018-03-23 12:41:45 -06:00
CREDITS	9p: remove Ron Minnich from MAINTAINERS	2018-08-17 16:20:26 -07:00
Kbuild	Kbuild updates for v4.15	2017-11-17 17:45:29 -08:00
Kconfig	kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt	2018-08-02 08:06:55 +09:00
MAINTAINERS	MAINTAINERS: Add Sasha as a stable branch maintainer	2018-12-01 09:37:25 +01:00
Makefile	Linux 4.19.24	2019-02-20 10:25:50 +01:00
README	Docs: Added a pointer to the formatted docs to README	2018-03-21 09:02:53 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.