From: Zqiang <qiang.zh...@windriver.com> 1/1 [ Author: He Zhe Email: zhe...@windriver.com Subject: eventfd: Enlarge recursion limit to allow vhost to work Date: Fri, 5 Jun 2020 16:32:18 +0800
commit 85f0a97f3aac6bb2c9549af607843644dd2ef5c7 upstream [linux-yocto] Upstream link: https://lore.kernel.org/lkml/20200410114720.24838-1-zhe...@windriver.com/ commit b5e683d5cab8 ("eventfd: track eventfd_signal() recursion depth") introduces a percpu counter that tracks the percpu recursion depth and warn if it greater than zero, to avoid potential deadlock and stack overflow. However sometimes different eventfds may be used in parallel. Specifically, when heavy network load goes through kvm and vhost, working as below, it would trigger the following call trace. - 100.00% - 66.51% ret_from_fork kthread - vhost_worker - 33.47% handle_tx_kick handle_tx handle_tx_copy vhost_tx_batch.isra.0 vhost_add_used_and_signal_n eventfd_signal - 33.05% handle_rx_net handle_rx vhost_add_used_and_signal_n eventfd_signal - 33.49% ioctl entry_SYSCALL_64_after_hwframe do_syscall_64 __x64_sys_ioctl ksys_ioctl do_vfs_ioctl kvm_vcpu_ioctl kvm_arch_vcpu_ioctl_run vmx_handle_exit handle_ept_misconfig kvm_io_bus_write __kvm_io_bus_write eventfd_signal 001: WARNING: CPU: 1 PID: 1503 at fs/eventfd.c:73 eventfd_signal+0x85/0xa0 ---- snip ---- 001: Call Trace: 001: vhost_signal+0x15e/0x1b0 [vhost] 001: vhost_add_used_and_signal_n+0x2b/0x40 [vhost] 001: handle_rx+0xb9/0x900 [vhost_net] 001: handle_rx_net+0x15/0x20 [vhost_net] 001: vhost_worker+0xbe/0x120 [vhost] 001: kthread+0x106/0x140 001: ? log_used.part.0+0x20/0x20 [vhost] 001: ? kthread_park+0x90/0x90 001: ret_from_fork+0x35/0x40 001: ---[ end trace 0000000000000003 ]--- This patch enlarges the limit to 1 which is the maximum recursion depth we have found so far. Signed-off-by: He Zhe <zhe...@windriver.com> Signed-off-by: Bruce Ashfield <bruce.ashfi...@gmail.com> [CE: backport of 85f0a97f3aac from v5.4 branch of linux-yocto] Signed-off-by: Catalin Enache <catalin.ena...@windriver.com> ] Signed-off-by: Zqiang <qiang.zh...@windriver.com> --- fs/eventfd.c | 2 +- include/linux/eventfd.h | 2 ++ 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/eventfd.c b/fs/eventfd.c index df466ef81ddd..7a5cbec9e843 100644 --- a/fs/eventfd.c +++ b/fs/eventfd.c @@ -71,7 +71,7 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) * it returns true, the eventfd_signal() call should be deferred to a * safe context. */ - if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count))) + if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count) > EFD_WAKE_COUNT_MAX)) return 0; spin_lock_irqsave(&ctx->wqh.lock, flags); diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h index dc4fd8a6644d..db050fb99e0b 100644 --- a/include/linux/eventfd.h +++ b/include/linux/eventfd.h @@ -29,6 +29,8 @@ #define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK) #define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE) +/* This is the maximum recursion depth we find so far */ +#define EFD_WAKE_COUNT_MAX 1 struct eventfd_ctx; struct file; -- 2.29.2
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