In message: [linux-yocto][linux-yocto v5.10][PATCH] eventfd: Enlarge recursion limit to allow vhost to work on 28/06/2021 [email protected] wrote:
> From: Zqiang <[email protected]> > > 1/1 [ > Author: He Zhe > Email: [email protected] > 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/[email protected]/ I was reading the thread on lore, and it isn't clear to me what is the latest status. Does this problem show more easily under preempt-rt, but is not a preempt-rt only fix ? I'm just trying to confirm that you are targeting this at v5.10/standard/base. You first submitted this a year ago, and it still isn't applied upstream. And Juri was seeing the same warning. There was a recent series posted that had a similar change to your v1, but you've resent this patch (v2?) as part of that effort .. but still no answer on the change. Also note, I just pushed 5.13 as the start of the new release kernel, since this is in mainline still, I assume I can apply this to those branches as well. Bruce > > 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 <[email protected]> > Signed-off-by: Bruce Ashfield <[email protected]> > [CE: backport of 85f0a97f3aac from v5.4 branch of linux-yocto] > Signed-off-by: Catalin Enache <[email protected]> > ] > > Signed-off-by: Zqiang <[email protected]> > --- > 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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