From: Kuniyuki Iwashima kuniyu@amazon.co.jp
commit f485922d8fe4e44f6d52a5bb95a603b7c65554bb upstream.
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@amazon.co.jp Link: https://lkml.kernel.org/r/20220322002653.33865-2-kuniyu@amazon.co.jp Fixes: 3b844826b6c6 ("pipe: avoid unnecessary EPOLLET wakeups under normal loads") Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.co.jp Cc: Alexander Duyck alexander.h.duyck@intel.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Davidlohr Bueso dave@stgolabs.net Cc: Kuniyuki Iwashima kuni1840@gmail.com Cc: "Soheil Hassas Yeganeh" soheil@google.com Cc: "Sridhar Samudrala" sridhar.samudrala@intel.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/pipe.c | 2 +- include/linux/pipe_fs_i.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
--- a/fs/pipe.c +++ b/fs/pipe.c @@ -652,7 +652,7 @@ 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 +++ b/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;