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freebsd-dev/sys/kern
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Konstantin Belousov 5975e53d40 Fix a race in vm_page_busy_sleep(9). 
Suppose that we have an exclusively busy page, and a thread which can
accept shared-busy page.  In this case, typical code waiting for the
page xbusy state to pass is
again:
	VM_OBJECT_WLOCK(object);
	...
	if (vm_page_xbusied(m)) {
		vm_page_lock(m);
 		VM_OBJECT_WUNLOCK(object);    <---1
		vm_page_busy_sleep(p, "vmopax");
 		goto again;
	}

Suppose that the xbusy state owner locked the object, unbusied the
page and unlocked the object after we are at the line [1], but before we
executed the load of the busy_lock word in vm_page_busy_sleep().  If it
happens that there is still no waiters recorded for the busy state,
the xbusy owner did not acquired the page lock, so it proceeded.

More, suppose that some other thread happen to share-busy the page
after xbusy state was relinquished but before the m->busy_lock is read
in vm_page_busy_sleep().  Again, that thread only needs vm_object lock
to proceed.  Then, vm_page_busy_sleep() reads busy_lock value equal to
the VPB_SHARERS_WORD(1).

In this case, all tests in vm_page_busy_sleep(9) pass and we are going
to sleep, despite the page being share-busied.

Update check for m->busy_lock == VPB_UNBUSIED in vm_page_busy_sleep(9)
to also accept shared-busy state if we only wait for the xbusy state to
pass.

Merge sequential if()s with the same 'then' clause in
vm_page_busy_sleep().

Note that the current code does not share-busy pages from parallel
threads, the only way to have more that one sbusy owner is right now
is to recurse.

Reported and tested by:	pho (previous version)
Reviewed by:	alc, markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D8196
2016-10-13 14:41:05 +00:00
..
bus_if.m INTRNG: Rework handling with resources. Partially revert r301453. 2016-08-19 10:52:39 +00:00
capabilities.conf Update capabilities.conf comment 2016-09-08 14:04:04 +00:00
clock_if.m
cpufreq_if.m
device_if.m Import the 'iflib' API library for network drivers. From the author: 2016-05-18 04:35:58 +00:00
genassym.sh genassym.sh: call nm(1) with NMFLAGS. 2015-08-14 22:57:13 +00:00
imgact_aout.c Implement vsyscall hack. Prior to 2.13 glibc uses vsyscall 2016-01-09 20:18:53 +00:00
imgact_binmisc.c sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
imgact_elf32.c
imgact_elf64.c
imgact_elf.c Style. 2016-10-04 15:23:03 +00:00
imgact_gzip.c Implement lockless resource limits. 2015-06-10 10:48:12 +00:00
imgact_shell.c
inflate.c ANSIfy inflate.c 2016-10-04 17:57:30 +00:00
init_main.c Remove assumptions in MI code that the BSP is CPU 0. 2016-07-11 21:25:28 +00:00
init_sysent.c Regnerate after r305140, getdtablesize in capability mode 2016-08-31 18:37:51 +00:00
kern_acct.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_alq.c Use SI_SUB_LAST instead of SI_SUB_SMP as the "catch-all" subsystem. 2016-03-11 23:18:06 +00:00
kern_clock.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_clocksource.c Add an EARLY_AP_STARTUP option to start APs earlier during boot. 2016-05-14 18:22:52 +00:00
kern_condvar.c cv: do a lockless check for no waiters in cv_signal and cv_broadcastpri 2016-09-06 17:16:59 +00:00
kern_conf.c Provide yet another KPI for cdev creation, make_dev_s(9). 2016-01-07 20:08:02 +00:00
kern_cons.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_context.c
kern_cpu.c Add an EARLY_AP_STARTUP option to start APs earlier during boot. 2016-05-14 18:22:52 +00:00
kern_cpuset.c Add more fine-grained kernel options for NUMA support. 2016-04-09 13:58:04 +00:00
kern_ctf.c
kern_descrip.c Give the user a clue as to which process hit maxfiles. 2016-09-24 22:56:13 +00:00
kern_dtrace.c
kern_dump.c kernel: use our nitems() macro when it is available through param.h. 2016-04-19 23:48:27 +00:00
kern_environment.c Create wrappers for uint64_t and int64_t for the tunables. While not 2016-04-15 03:09:55 +00:00
kern_et.c
kern_event.c Another issue reported on http://seclists.org/oss-sec/2016/q3/68 is 2016-07-16 13:24:58 +00:00
kern_exec.c Eliminate unneeded vm_page_xbusy() and vm_page_xunbusy() operations when 2016-08-14 22:00:45 +00:00
kern_exit.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_fail.c Fix some cosmetic issues in kern_fail.c omitted from r296927. 2016-06-09 13:17:08 +00:00
kern_ffclock.c kernel: use our nitems() macro when it is available through param.h. 2016-04-19 23:48:27 +00:00
kern_fork.c Add PROC_TRAPCAP procctl(2) controls and global sysctl kern.trap_enocap. 2016-09-21 08:23:33 +00:00
kern_gzio.c
kern_hhook.c Get closer to a VIMAGE network stack teardown from top to bottom rather 2016-06-21 13:48:49 +00:00
kern_idle.c
kern_intr.c The part of r285680 which removed release semantic for two stores to 2015-07-21 14:39:34 +00:00
kern_jail.c Move IPv4-specific jail functions to new file netinet/in_jail.c 2016-08-09 02:16:21 +00:00
kern_khelp.c
kern_kthread.c Re-schedule signals after kthread exits, since apparently there are 2016-08-10 13:47:12 +00:00
kern_ktr.c Fix the logic in the ddb command 'show ktr /a'. Prior to r118269 it would 2016-01-31 17:32:20 +00:00
kern_ktrace.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_linker.c kern_linker: Handle module-loading failures in preloaded .ko files 2016-10-13 02:06:23 +00:00
kern_lock.c Microoptimize locking primitives by avoiding unnecessary atomic ops. 2016-06-01 18:32:20 +00:00
kern_lockf.c Fix LINT building. 2016-09-18 07:37:00 +00:00
kern_lockstat.c Consistently use a reader/writer flag for lockstat probes in rwlock(9) and 2015-07-19 22:24:33 +00:00
kern_loginclass.c Speed up rctl operation with large rulesets, by holding the lock 2015-11-15 12:10:51 +00:00
kern_malloc.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_mbuf.c Import the 'iflib' API library for network drivers. From the author: 2016-05-18 04:35:58 +00:00
kern_mib.c Provide kern.maxphys sysctl, which returns MAXPHYS. Naming matches NetBSD. 2016-09-29 23:07:28 +00:00
kern_module.c Provide better debug message on kernel module name clash. 2015-10-10 09:21:55 +00:00
kern_mtxpool.c sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
kern_mutex.c Make no assertions about mutex state when the scheduler is stopped. 2016-09-26 15:30:30 +00:00
kern_ntptime.c Fix a bug in r302252. 2016-07-27 11:40:06 +00:00
kern_numa.c Add an initial NUMA affinity/policy configuration for threads and processes. 2015-07-11 15:21:37 +00:00
kern_osd.c osd(9): Change array pointer to array pointer type from void* 2016-04-26 19:57:35 +00:00
kern_physio.c Add four new RCTL resources - readbps, readiops, writebps and writeiops, 2016-04-07 04:23:25 +00:00
kern_pmc.c
kern_poll.c
kern_priv.c
kern_proc.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_procctl.c Add the foundation copyrights to procctl kernel sources. 2016-09-23 12:32:20 +00:00
kern_prot.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_racct.c Get rid of rctl_lock; use racct_lock where appropriate. The fast paths 2016-04-21 16:22:52 +00:00
kern_rangelock.c
kern_rctl.c sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
kern_resource.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_rmlock.c sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
kern_rwlock.c locks: fix compilation for KDTRACE_HOOKS && !ADAPTIVE_* case 2016-08-02 03:05:59 +00:00
kern_sdt.c
kern_sema.c
kern_sendfile.c Fix regression from r297400, which truncates headers in case of low socket 2016-09-22 20:34:44 +00:00
kern_sharedpage.c Split kerne timekeep ABI structure vdso_sv_tk out of the struct 2015-11-23 07:09:35 +00:00
kern_shutdown.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_sig.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_switch.c
kern_sx.c locks: fix sx compilation on mips after r303643 2016-08-03 09:15:10 +00:00
kern_synch.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_syscalls.c Implement lockless resource limits. 2015-06-10 10:48:12 +00:00
kern_sysctl.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_tc.c Implement userspace gettimeofday(2) with HPET timecounter. 2016-08-17 09:52:09 +00:00
kern_thr.c Add a mask of optional ptrace() events. 2016-07-15 15:32:09 +00:00
kern_thread.c Rewrite subr_sleepqueue.c use of callouts to not depend on the 2016-07-28 09:09:55 +00:00
kern_time.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_timeout.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
kern_umtx.c In both do_rw_wrlock() and do_rw_rdlock() after r304808, do not 2016-08-25 19:15:02 +00:00
kern_uuid.c
kern_xxx.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
ksched.c Use P1B_PRIO_MAX to designate max posix priority for the RR/FIFO 2015-08-30 18:02:57 +00:00
link_elf_obj.c sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
link_elf.c kern: for pointers replace 0 with NULL. 2016-04-15 16:10:11 +00:00
linker_if.m sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
Make.tags.inc Bring the tags and links entries for amd64 up to date. 2015-10-27 22:59:24 +00:00
Makefile Don't create pointless backups of generated files in "make sysent". 2016-07-28 21:29:04 +00:00
makesyscalls.sh Annotate syscall provider pointer arguments with the "userland" keyword. 2016-09-22 04:49:31 +00:00
md4c.c crypto routines: Hint minimum buffer sizes to the compiler 2016-05-26 19:29:29 +00:00
md5c.c crypto routines: Hint minimum buffer sizes to the compiler 2016-05-26 19:29:29 +00:00
msi_if.m Introduce MSI and MSI-X support to intrng. This adds a new msi device 2016-05-16 09:11:40 +00:00
p1003_1b.c In preparation for switching linuxulator to the use the native 1:1 2015-05-24 14:44:06 +00:00
pic_if.m INTRNG: Rework handling with resources. Partially revert r301453. 2016-08-19 10:52:39 +00:00
posix4_mib.c posix4_mib: Don't overrun facility_initialized array 2016-04-27 00:10:32 +00:00
sched_4bsd.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
sched_ule.c Get rid of struct proc p_sched and struct thread td_sched pointers. 2016-06-05 17:04:03 +00:00
serdev_if.m
stack_protector.c Use nitems() macro instead of __arraycount() 2015-06-16 20:19:00 +00:00
subr_acl_nfs4.c Expose an interface to determine if an ACE is inherited. 2015-09-04 00:14:20 +00:00
subr_acl_posix1e.c
subr_autoconf.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_blist.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_bufring.c
subr_bus_dma.c Fix a bug introduced in r291716: 2016-01-11 20:38:39 +00:00
subr_bus.c Make device_quiet() an attachment property. 2016-09-12 18:06:42 +00:00
subr_busdma_bufalloc.c Fix printf format to allow for bus_size_t not being u_long on all platforms. 2015-10-20 03:25:17 +00:00
subr_capability.c capsicum: plug spurious memset in __cap_rights_init 2015-12-01 02:48:42 +00:00
subr_clock.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_counter.c Free the temporary buffer in sysctl_handle_counter_u64_array(). 2016-03-15 00:21:32 +00:00
subr_devmap.c Include machine/acle-compat.h in cdefs.h on arm if the compiler doesn't 2016-05-25 19:44:26 +00:00
subr_devstat.c Add support for managing Shingled Magnetic Recording (SMR) drives. 2016-05-19 14:08:36 +00:00
subr_disk.c
subr_dummy_vdso_tc.c
subr_eventhandler.c
subr_fattime.c
subr_firmware.c Create a dedicated function for ensuring that cdir and rdir are populated. 2015-07-11 16:22:48 +00:00
subr_gtaskqueue.c Fix bug where malloc(.., M_NOWAIT) return value is not checked, Change to 2016-10-11 14:08:53 +00:00
subr_hash.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_hints.c
subr_intr.c INTRNG - fix MSI/MSIX release path 2016-10-11 17:00:29 +00:00
subr_kdb.c
subr_kobj.c
subr_lock.c Implement trivial backoff for locking primitives. 2016-08-01 21:48:37 +00:00
subr_log.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_mbpool.c sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
subr_mchain.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_module.c preload_search_info: make sure mod is set 2015-08-21 15:57:57 +00:00
subr_msgbuf.c sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
subr_param.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_pcpu.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_pctrie.c sys: extend use of the howmany() macro when available. 2016-04-26 15:38:17 +00:00
subr_power.c
subr_prf.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_prof.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_rman.c Add new bus methods for mapping resources. 2016-05-20 17:57:47 +00:00
subr_rtc.c Make resettodr_lock accessible outside subr_rtc.c. Protect 2016-09-21 10:15:08 +00:00
subr_sbuf.c Fail the sbuf if vsnprintf(3) fails. 2015-10-02 09:23:14 +00:00
subr_scanf.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_sfbuf.c
subr_sglist.c Add sglist functions for working with arrays of VM pages. 2016-05-20 23:28:43 +00:00
subr_sleepqueue.c Micro-optimize sleepq_signal(). 2016-09-04 00:29:48 +00:00
subr_smp.c Reduce duplicated logic for !SMP 2016-08-30 19:26:07 +00:00
subr_stack.c Add support for a configurable output channel to witness(4). 2015-11-19 05:56:59 +00:00
subr_syscall.c Add PROC_TRAPCAP procctl(2) controls and global sysctl kern.trap_enocap. 2016-09-21 08:23:33 +00:00
subr_taskqueue.c While draining a timeout task prevent the taskqueue_enqueue_timeout() 2016-09-29 10:38:20 +00:00
subr_terminal.c
subr_trap.c The assertion re-added in r302614 was triggered when stopping signal 2016-07-18 10:53:47 +00:00
subr_turnstile.c Finish r173600. There is no need to test a condition if both cases 2016-02-10 21:16:37 +00:00
subr_uio.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
subr_unit.c Fix build of kern/subr_unit.c, broken by r300539 2016-05-24 00:14:58 +00:00
subr_vmem.c subr_vmem: Fix double-free in error case of vmem_create 2016-05-11 23:16:11 +00:00
subr_witness.c cache: get rid of the global lock 2016-09-23 04:45:11 +00:00
sys_capability.c Add PROC_TRAPCAP procctl(2) controls and global sysctl kern.trap_enocap. 2016-09-21 08:23:33 +00:00
sys_generic.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
sys_pipe.c Generate syscall tables and update pipe() implementation after r302094. 2016-06-22 21:18:19 +00:00
sys_procdesc.c Hide the boottime and bootimebin globals, provide the getboottime(9) 2016-07-27 11:08:59 +00:00
sys_process.c Don't set P2_PTRACE_FSTP in a process that invokes ptrace(PT_TRACE_ME). 2016-08-19 17:57:14 +00:00
sys_socket.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
syscalls.c Remove the obsolete and unused openbsd_poll system call. (Phase 2) 2016-08-18 10:54:39 +00:00
syscalls.master Remove unusedd and obsolete openbsd_poll system call. (Phase 1) 2016-08-18 10:50:40 +00:00
systrace_args.c Regenerate syscall provider argument strings. 2016-09-22 04:50:03 +00:00
sysv_ipc.c
sysv_msg.c Remove a comment that was part of copied code, and is misleading in 2016-06-09 15:34:33 +00:00
sysv_sem.c sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
sysv_shm.c Add shmatt_t. 2016-07-26 17:23:49 +00:00
tty_compat.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
tty_info.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
tty_inq.c
tty_outq.c
tty_pts.c sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
tty_tty.c tty: replace several curthread->td_proc with stored curproc 2015-07-06 18:53:56 +00:00
tty_ttydisc.c Don't clear the software flow control flag before draining for last 2016-01-26 14:46:39 +00:00
tty.c sys/kern: spelling fixes in comments. 2016-04-29 22:15:33 +00:00
uipc_accf.c Use correct size type in do_setopt_accept_filter 2016-10-12 00:56:49 +00:00
uipc_debug.c Refactor the AIO subsystem to permit file-type-specific handling and 2016-03-01 18:12:14 +00:00
uipc_domain.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
uipc_mbuf2.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
uipc_mbuf.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
uipc_mbufhash.c
uipc_mqueue.c Use the new PR_METHOD_REMOVE to clean up jail handling in POSIX 2016-04-25 04:36:54 +00:00
uipc_sem.c Clean up some style(9) violations. 2016-04-14 17:07:26 +00:00
uipc_shm.c Eliminate unneeded vm_page_xbusy() and vm_page_xunbusy() operations when 2016-08-14 22:00:45 +00:00
uipc_sockbuf.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
uipc_socket.c Adjust the sopt_val pointer on bigendian systems (e.g. MIPS64EB). 2016-09-22 12:41:53 +00:00
uipc_syscalls.c Revert r306337. dhw@ reproted a panic which seems related to this and bde@ has 2016-09-26 15:45:30 +00:00
uipc_usrreq.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
vfs_acl.c Replace struct filedesc argument in getvnode with struct thread 2015-06-16 13:09:18 +00:00
vfs_aio.c Remove duplicated code. 2016-08-17 10:14:22 +00:00
vfs_bio.c Fix a race in vm_page_busy_sleep(9). 2016-10-13 14:41:05 +00:00
vfs_cache.c Limit scope of the optimization in r306608 to dounmount() caller only. 2016-10-07 11:38:28 +00:00
vfs_cluster.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
vfs_default.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
vfs_export.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
vfs_extattr.c Replace struct filedesc argument in getvnode with struct thread 2015-06-16 13:09:18 +00:00
vfs_hash.c Add vfs_hash_ref(9) function, which finds a vnode by the hash value 2016-05-11 06:32:22 +00:00
vfs_init.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
vfs_lookup.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
vfs_mount.c vfs: assert empty tmp free list on unmount 2016-10-08 13:38:05 +00:00
vfs_mountroot.c Limit scope of the optimization in r306608 to dounmount() caller only. 2016-10-07 11:38:28 +00:00
vfs_subr.c vfs: clear the tmp free list flag before taking the free vnode list lock 2016-10-08 13:36:59 +00:00
vfs_syscalls.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
vfs_vnops.c Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00
vnode_if.src Renumber license clauses in sys/kern to avoid skipping #3 2016-09-15 13:16:20 +00:00