Re: [PATCH] trace : use kvmalloc instead of kmalloc

[Zhaoyang Huang]

On Thu, Jul 30, 2020 at 9:58 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Thu, 30 Jul 2020 19:04:12 +0800
> Zhaoyang Huang <huangzhaoyang@xxxxxxxxx> wrote:
>
> > High order memory stuff within trace could introduce OOM, use kvmalloc instead.
> >
> > Please find the bellowing for the call stack we run across in an android system. The scenario happens when traced_probes is woken up to get a large quantity of trace even if free memory is even higher than watermark_low.
>
> Please limit your column width in the description of patches to 76
> characters.
>
> >
> > traced_probes invoked oom-killer: gfp_mask=0x140c0c0(GFP_KERNEL|__GFP_COMP|__GFP_ZERO), nodemask=(null),  order=2, oom_score_adj=-1
> >
>
> What does this traced_probes thing do?
traced_probes is an android exe which reads ftrace and writes them to
files. I think kzalloc works fine for most of context but will cause
OOM in high ratio ftrace access in memory constraint system, like
mobilephone etc.
>
> > traced_probes cpuset=system-background mems_allowed=0
> > CPU: 3 PID: 588 Comm: traced_probes Tainted: G        W  O    4.14.181 #1
> > Hardware name: Generic DT based system
> > (unwind_backtrace) from [<c010d824>] (show_stack+0x20/0x24)
> > (show_stack) from [<c0b2e174>] (dump_stack+0xa8/0xec)
> > (dump_stack) from [<c027d584>] (dump_header+0x9c/0x220)
> > (dump_header) from [<c027cfe4>] (oom_kill_process+0xc0/0x5c4)
> > (oom_kill_process) from [<c027cb94>] (out_of_memory+0x220/0x310)
> > (out_of_memory) from [<c02816bc>] (__alloc_pages_nodemask+0xff8/0x13a4)
> > (__alloc_pages_nodemask) from [<c02a6a1c>] (kmalloc_order+0x30/0x48)
> > (kmalloc_order) from [<c02a6a64>] (kmalloc_order_trace+0x30/0x118)
> > (kmalloc_order_trace) from [<c0223d7c>] (tracing_buffers_open+0x50/0xfc)
> > (tracing_buffers_open) from [<c02e6f58>] (do_dentry_open+0x278/0x34c)
> > (do_dentry_open) from [<c02e70d0>] (vfs_open+0x50/0x70)
> > (vfs_open) from [<c02f7c24>] (path_openat+0x5fc/0x169c)
> > (path_openat) from [<c02f75c4>] (do_filp_open+0x94/0xf8)
> > (do_filp_open) from [<c02e7650>] (do_sys_open+0x168/0x26c)
> > (do_sys_open) from [<c02e77bc>] (SyS_openat+0x34/0x38)
> > (SyS_openat) from [<c0108bc0>] (ret_fast_syscall+0x0/0x28)
> >
> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> > ---
> > changes since v1: change kfree to kvfree
> > ---
> >  kernel/trace/trace.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index ca1ee65..8d70c79 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -6891,7 +6891,7 @@ static int tracing_buffers_open(struct inode *inode, struct file *filp)
> >       if (trace_array_get(tr) < 0)
> >               return -ENODEV;
> >
> > -     info = kzalloc(sizeof(*info), GFP_KERNEL);
> > +     info = kvmalloc(sizeof(*info), GFP_KERNEL);
>
> The above is a bug. It converts kzalloc() to kvmalloc() instead of
> kvzalloc().
fixed and resend with patch v2
>
> -- Steve
>
>
>
> >       if (!info) {
> >               trace_array_put(tr);
> >               return -ENOMEM;
> > @@ -7017,7 +7017,7 @@ static int tracing_buffers_release(struct inode *inode, struct file *file)
> >       if (info->spare)
> >               ring_buffer_free_read_page(iter->trace_buffer->buffer,
> >                                          info->spare_cpu, info->spare);
> > -     kfree(info);
> > +     kvfree(info);
> >
> >       mutex_unlock(&trace_types_lock);
> >
>