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qemu-e2k/util
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Paolo Bonzini 050de36b13 coroutine-lock: Reimplement CoRwlock to fix downgrade bug 
An invariant of the current rwlock is that if multiple coroutines hold a
reader lock, all must be runnable. The unlock implementation relies on
this, choosing to wake a single coroutine when the final read lock
holder exits the critical section, assuming that it will wake a
coroutine attempting to acquire a write lock.

The downgrade implementation violates this assumption by creating a
read lock owning coroutine that is exclusively runnable - any other
coroutines that are waiting to acquire a read lock are *not* made
runnable when the write lock holder converts its ownership to read
only.

More in general, the old implementation had lots of other fairness bugs.
The root cause of the bugs was that CoQueue would wake up readers even
if there were pending writers, and would wake up writers even if there
were readers.  In that case, the coroutine would go back to sleep *at
the end* of the CoQueue, losing its place at the head of the line.

To fix this, keep the queue of waiters explicitly in the CoRwlock
instead of using CoQueue, and store for each whether it is a
potential reader or a writer.  This way, downgrade can look at the
first queued coroutines and wake it only if it is a reader, causing
all other readers in line to be released in turn.

Reported-by: David Edmondson <david.edmondson@oracle.com>
Reviewed-by: David Edmondson <david.edmondson@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20210325112941.365238-5-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
 		2021-03-31 10:44:21 +01:00
..
aio-posix.c qmp: Move dispatcher to a coroutine 2020-10-09 07:08:20 +02:00
aio-posix.h
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aio-wait.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
aio-win32.c qmp: fix aio_poll() assertion failure on Windows 2020-11-03 16:24:56 +01:00
aiocb.c
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async.c util/async: Add aio_co_reschedule_self() 2020-10-09 07:08:20 +02:00
atomic64.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
base64.c nomaintainer: Fix Lesser GPL version number 2020-11-15 17:04:40 +01:00
bitmap.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
bitops.c
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block-helpers.c block: move logical block size check function to a common utility function 2020-10-23 13:42:16 +01:00
block-helpers.h block: move logical block size check function to a common utility function 2020-10-23 13:42:16 +01:00
buffer.c nomaintainer: Fix Lesser GPL version number 2020-11-15 17:04:40 +01:00
bufferiszero.c
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cacheflush.c util/cacheflush: Fix error generated by clang 2021-01-21 13:00:41 +01:00
cacheinfo.c util: Enhance flush_icache_range with separate data pointer 2021-01-07 05:09:41 -10:00
compatfd.c util/compatfd.c: Only include <sys/syscall.h> if CONFIG_SIGNALFD 2020-07-13 14:36:10 +01:00
coroutine-sigaltstack.c coroutine-sigaltstack: Add SIGUSR2 mutex 2021-01-26 14:36:37 +01:00
coroutine-ucontext.c Remove the CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE switch 2020-07-13 11:40:52 +02:00
coroutine-win32.c
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crc-ccitt.c util: Add CRC16 (CCITT) calculation routines 2021-01-24 20:10:54 +01:00
crc32c.c
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cutils.c utils: Work around mingw strto*l bug with 0x 2021-03-24 14:25:41 +00:00
dbus.c
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drm.c util/drm: make portable by avoiding struct dirent d_type 2020-07-13 14:36:10 +01:00
envlist.c
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error.c
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event_notifier-posix.c event_notifier: Set ->initialized earlier in event_notifier_init() 2021-02-16 17:15:39 +01:00
event_notifier-win32.c
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fdmon-epoll.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
fdmon-io_uring.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
fdmon-poll.c fdmon-poll: reset npfd when upgrading to fdmon-epoll 2020-09-23 13:45:52 +01:00
fifo8.c utils/fifo8: change fatal errors from abort() to assert() 2021-02-07 20:38:20 +00:00
filemonitor-inotify.c nomaintainer: Fix Lesser GPL version number 2020-11-15 17:04:40 +01:00
filemonitor-stub.c nomaintainer: Fix Lesser GPL version number 2020-11-15 17:04:40 +01:00
getauxval.c
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guest-random.c
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hbitmap.c
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hexdump.c util/hexdump: introduce qemu_hexdump_line() 2020-09-29 02:14:30 -04:00
host-utils.c
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id.c net: Use id_generate() in the network subsystem, too 2021-03-09 21:47:45 +01:00
iov.c util/iov: make qemu_iovec_init_extended() honest 2021-02-03 08:00:33 -06:00
iova-tree.c
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keyval.c keyval: Use GString to accumulate value strings 2020-12-19 10:39:23 +01:00
lockcnt.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
log.c nomaintainer: Fix Lesser GPL version number 2020-11-15 17:04:40 +01:00
main-loop.c qtest: delete superfluous inclusions of qtest.h 2021-03-09 06:03:53 +01:00
memfd.c
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meson.build migration: introduce UFFD-WP low-level interface helpers 2021-02-08 11:19:51 +00:00
mmap-alloc.c memory: alloc RAM from file at offset 2021-02-09 20:53:56 +00:00
module.c s390x: modularize virtio-gpu-ccw 2021-03-26 09:33:50 +01:00
notify.c
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nvdimm-utils.c Clean up includes 2020-12-10 17:16:44 +01:00
osdep.c Pull request trivial patches 20200919 2020-09-22 15:42:23 +01:00
oslib-posix.c memory: alloc RAM from file at offset 2021-02-09 20:53:56 +00:00
oslib-win32.c util/oslib-win32: Fix _aligned_malloc() arguments order 2021-01-11 14:59:21 +01:00
pagesize.c
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path.c
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qdist.c
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qemu-co-shared-resource.c
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qemu-config.c qemu-config: add error propagation to qemu_config_parse 2021-03-06 11:41:54 +01:00
qemu-coroutine-io.c
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qemu-coroutine-lock.c coroutine-lock: Reimplement CoRwlock to fix downgrade bug 2021-03-31 10:44:21 +01:00
qemu-coroutine-sleep.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
qemu-coroutine.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
qemu-error.c error: rename error_with_timestamp to message_with_timestamp 2021-02-01 10:50:55 +00:00
qemu-openpty.c util/qemu-openpty.c: Don't assume pty.h is glibc-only 2020-07-13 14:36:09 +01:00
qemu-option.c qemu-option: do not suggest using the delay option 2021-03-06 11:42:57 +01:00
qemu-print.c monitor: Use getter/setter functions for cur_mon 2020-10-09 07:08:19 +02:00
qemu-progress.c util/: fix some comment spelling errors 2020-09-17 20:38:42 +02:00
qemu-sockets.c sockets: Make abstract UnixSocketAddress depend on CONFIG_LINUX 2020-11-03 13:17:25 +00:00
qemu-thread-common.h
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qemu-thread-posix.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
qemu-thread-win32.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
qemu-timer-common.c semihosting: Implement SYS_ELAPSED and SYS_TICKFREQ 2021-01-18 10:05:06 +00:00
qemu-timer.c ppc patch queue for 2021-03-10 2021-03-12 11:30:55 +00:00
qht.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
qsp.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
range.c
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rcu.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
readline.c readline: Fix possible array index out of bounds in readline_hist_add() 2021-01-04 11:13:39 +00:00
selfmap.c
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stats64.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
sys_membarrier.c
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systemd.c
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thread-pool.c
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throttle.c Remove superfluous timer_del() calls 2021-01-08 15:13:38 +00:00
timed-average.c
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trace-events migration: introduce UFFD-WP low-level interface helpers 2021-02-08 11:19:51 +00:00
trace.h trace: switch position of headers to what Meson requires 2020-08-21 06:18:24 -04:00
unicode.c
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uri.c
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userfaultfd.c migration: introduce UFFD-WP low-level interface helpers 2021-02-08 11:19:51 +00:00
uuid.c
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vfio-helpers.c Pull request for 5.2 2020-11-23 13:03:13 +00:00
vhost-user-server.c util/vhost-user-server: move header to include/ 2020-10-23 13:42:16 +01:00
yank.c Introduce yank feature 2021-01-13 10:21:17 +01:00