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freebsd with flexible iflib nic queues
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Mark Johnston 6d3f74a14a sched_ule: Fix racy loads of pc_curthread 
Thread switching used to be atomic with respect to the current CPU's
tdq lock.  Since commit 686bcb5c14 that is no longer the case.  Now
sched_switch() does this:

1.  lock tdq (might already be locked)
2.  maybe put the current thread in the tdq, choose a new thread to run
2a. update tdq_lowpri
3.  unlock tdq
4.  switch CPU context, update curthread

Some code paths in ULE will load pc_curthread from a remote CPU with
that CPU's tdq lock held, usually to inspect its priority.  But, as of
the aforementioned commit this is racy.

The problem I noticed is in tdq_notify(), which optionally sends an IPI
to a remote CPU when a new thread is added to its runqueue.  If the new
thread's priority is higher (lower) than the currently running thread's
priority, then we deliver an IPI.  But inspecting
pc_curthread->td_priority doesn't work, since pc_curthread might be
between steps 3 and 4 above.  If pc_curthread's priority is higher than
that of the newly added thread, but pc_curthread is switching to a
lower-priority thread, then tdq_notify() might fail to deliever an IPI,
leaving a high priority thread stuck on the runqueue for longer than it
should.  This can cause multi-millisecond stalls in
interactive/ithread/realtime threads.

Fix this problem by modifying tdq_add() and tdq_move() to return the
value of tdq_lowpri before the addition of the new thread.  This ensures
that tdq_notify() has the correct priority value to compare against.

The other two uses of pc_curthread are susceptible to the same race.  To
fix the one in sched_rem()->tdq_setlowpri() we need to have an exact
value for curthread.  Thus, introduce a new tdq_curthread field to the
tdq which gets updated any time a new thread is selected to run on the
CPU.  Because this field is synchronized by the thread lock, its
priority reflects the correct lowpri value for the tdq.

PR:		264867
Fixes:		686bcb5c14 ("schedlock 4/4")
Reviewed by:	mav, kib, jhb
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D35736
2022-07-14 10:27:51 -04:00
.cirrus-ci Cirrus-CI: add some timing info on pkg install failure 2021-08-04 15:02:00 -04:00
.github .github: Attempt to fix and increase robustness of macOS action 2022-06-30 21:03:26 +01:00
bin date: attempt to more accurately describe year limitations with -v 2022-06-27 22:54:13 -05:00
cddl zfs: merge openzfs/zfs@cb01da680 2022-07-08 00:02:36 +02:00
contrib unbound: Vendor import 1.16.1 2022-07-13 12:30:14 -07:00
crypto OpenSSL: Merge OpenSSL 1.1.1q 2022-07-05 11:47:01 -04:00
etc Enable -Wwrite-strings 2022-06-29 14:08:54 -07:00
gnu libdialog: Bump shared library version to 10. 2021-10-27 09:30:24 -07:00
include Import OpenSSL 1.1.1q 2022-07-05 11:27:51 -04:00
kerberos5 pkgbase: Create a FreeBSD-kerberos package 2021-09-07 10:23:14 +02:00
lib msun: Rewrite function definitions with identifier lists 2022-07-12 13:17:47 +08:00
libexec rtld-elf: Fix leaks and wild frees in origin_subst 2022-07-12 17:47:47 +01:00
release release: increase IMAGE_SIZE for arm, arm64, riscv 2022-07-13 14:36:22 -04:00
rescue Fix conflict between libnvpair and libnv when building rescue binaries. 2022-05-24 23:59:33 +03:00
sbin ifconfig.8: cleanup reminiscence about long gone ppp(4) 2022-07-11 11:53:54 +07:00
secure OpenSSL: Regen manual pages for OpenSSL 1.1.1q 2022-07-05 12:01:07 -04:00
share inet.4 tcp.4 udp.4: Replace *CTL_* OID macro names with sysctl names 2022-07-14 08:50:13 -05:00
stand loader.efi: faults could try to print out call trace 2022-07-14 15:59:26 +03:00
sys sched_ule: Fix racy loads of pc_curthread 2022-07-14 10:27:51 -04:00
targets bintrans: move files to a new directory 2022-04-18 10:53:11 +02:00
tests pf tests: support packet size range in pft_ether.py 2022-07-11 19:55:26 +02:00
tools git-arc: Fix the -y option 2022-07-13 09:30:17 -04:00
usr.bin Improve usability of head(1) and tail(1): 2022-07-12 21:14:25 -07:00
usr.sbin certctl: Introduce a new -d <distbase> option 2022-07-14 01:23:42 +01:00
.arcconfig Remove history.immutable from .arcconfig 2021-04-13 12:36:25 +01:00
.arclint
.cirrus.yml Cirrus-CI: update image to FreeBSD 13.1 (latest release) 2022-06-02 15:25:36 -04:00
.clang-format clang-format: Add bitset loop macros 2021-09-21 12:08:01 -04:00
.gitattributes Add a basic clang-format configuration file 2019-06-07 15:23:52 +00:00
.gitignore gitignore: Ignore compile_commands.events.json 2022-05-30 10:43:25 -04:00
COPYRIGHT Welcome 2022, update copyrights. 2022-01-01 09:49:49 -07:00
LOCKS
MAINTAINERS Remove myself from bhyve maintenance; ENOTIME. 2021-11-19 07:09:30 +10:00
Makefile Switch to GCC 9 for the GCC tinderbox. 2022-05-20 10:16:57 -07:00
Makefile.inc1 Makefile.inc1: Fix -DNO_ROOT distributeworld certctl usage 2022-07-14 01:25:50 +01:00
Makefile.libcompat libcompat: Use WORLDTMP sysroot 2022-07-01 08:33:16 +01:00
Makefile.sys.inc
ObsoleteFiles.inc ObsoleteFiles: flowtable header deleted in 2017 2022-06-27 12:31:36 -07:00
README.md README.md: update gnu directory description 2021-12-17 08:45:31 -05:00
RELNOTES RELNOTES: Add an entry for boottrace(4) 2022-03-29 13:35:14 +02:00
UPDATING LinuxKPI: move pm_message_t from kernel.h to pm.h 2022-06-10 14:05:12 +00:00

README.md

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