The patch titled
Subject: pipe: make poll_usage boolean and annotate its access
has been added to the -mm tree. Its filename is
pipe-make-poll_usage-boolean-and-annotate-its-access.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/pipe-make-poll_usage-boolean-and-annotate-its-access.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/pipe-make-poll_usage-boolean-and-annotate-its-access.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Kuniyuki Iwashima <kuniyu@xxxxxxxxxxxx>
Subject: pipe: make poll_usage boolean and annotate its access
Patch series "Fix data-races around epoll reported by KCSAN."
This series suppresses a false positive KCSAN's message and fixes a real
data-race.
This patch (of 2):
pipe_poll() runs locklessly and assigns 1 to poll_usage. Once poll_usage
is set to 1, it never changes in other places. However, concurrent writes
of a value trigger KCSAN, so let's make KCSAN happy.
BUG: KCSAN: data-race in pipe_poll / pipe_poll
write to 0xffff8880042f6678 of 4 bytes by task 174 on cpu 3:
pipe_poll (fs/pipe.c:656)
ep_item_poll.isra.0 (./include/linux/poll.h:88 fs/eventpoll.c:853)
do_epoll_wait (fs/eventpoll.c:1692 fs/eventpoll.c:1806 fs/eventpoll.c:2234)
__x64_sys_epoll_wait (fs/eventpoll.c:2246 fs/eventpoll.c:2241 fs/eventpoll.c:2241)
do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
write to 0xffff8880042f6678 of 4 bytes by task 177 on cpu 1:
pipe_poll (fs/pipe.c:656)
ep_item_poll.isra.0 (./include/linux/poll.h:88 fs/eventpoll.c:853)
do_epoll_wait (fs/eventpoll.c:1692 fs/eventpoll.c:1806 fs/eventpoll.c:2234)
__x64_sys_epoll_wait (fs/eventpoll.c:2246 fs/eventpoll.c:2241 fs/eventpoll.c:2241)
do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 177 Comm: epoll_race Not tainted 5.17.0-58927-gf443e374ae13 #6
Hardware name: Red Hat KVM, BIOS 1.11.0-2.amzn2 04/01/2014
Link: https://lkml.kernel.org/r/20220322002653.33865-1-kuniyu@xxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20220322002653.33865-2-kuniyu@xxxxxxxxxxxx
Fixes: 3b844826b6c6 ("pipe: avoid unnecessary EPOLLET wakeups under normal loads")
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxxxx>
Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Kuniyuki Iwashima <kuni1840@xxxxxxxxx>
Cc: "Soheil Hassas Yeganeh" <soheil@xxxxxxxxxx>
Cc: "Sridhar Samudrala" <sridhar.samudrala@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/pipe.c | 2 +-
include/linux/pipe_fs_i.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
--- a/fs/pipe.c~pipe-make-poll_usage-boolean-and-annotate-its-access
+++ a/fs/pipe.c
@@ -653,7 +653,7 @@ pipe_poll(struct file *filp, poll_table
unsigned int head, tail;
/* Epoll has some historical nasty semantics, this enables them */
- pipe->poll_usage = 1;
+ WRITE_ONCE(pipe->poll_usage, true);
/*
* Reading pipe state only -- no need for acquiring the semaphore.
--- a/include/linux/pipe_fs_i.h~pipe-make-poll_usage-boolean-and-annotate-its-access
+++ a/include/linux/pipe_fs_i.h
@@ -71,7 +71,7 @@ struct pipe_inode_info {
unsigned int files;
unsigned int r_counter;
unsigned int w_counter;
- unsigned int poll_usage;
+ bool poll_usage;
struct page *tmp_page;
struct fasync_struct *fasync_readers;
struct fasync_struct *fasync_writers;
_
Patches currently in -mm which might be from kuniyu@xxxxxxxxxxxx are
pipe-make-poll_usage-boolean-and-annotate-its-access.patch
list-fix-a-data-race-around-ep-rdllist.patch
