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Date: Tue, 7 Nov 2017 11:03:55 +0800
From: Boqun Feng <boqun.feng@...il.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Andy Lutomirski <luto@...capital.net>,
Dave Watson <davejwatson@...com>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-api <linux-api@...r.kernel.org>,
Paul Turner <pjt@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Russell King <linux@....linux.org.uk>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
Ben Maurer <bmaurer@...com>, rostedt <rostedt@...dmis.org>,
Josh Triplett <josh@...htriplett.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [RFC PATCH v2 for 4.15 08/14] Provide cpu_opv system call
On Tue, Nov 07, 2017 at 02:40:37AM +0000, Mathieu Desnoyers wrote:
> ----- On Nov 6, 2017, at 9:07 PM, Boqun Feng boqun.feng@...il.com wrote:
>
> > On Mon, Nov 06, 2017 at 03:56:38PM -0500, Mathieu Desnoyers wrote:
> > [...]
> >> +static int cpu_op_pin_pages(unsigned long addr, unsigned long len,
> >> + struct page ***pinned_pages_ptr, size_t *nr_pinned,
> >> + int write)
> >> +{
> >> + struct page *pages[2];
> >> + int ret, nr_pages;
> >> +
> >> + if (!len)
> >> + return 0;
> >> + nr_pages = cpu_op_range_nr_pages(addr, len);
> >> + BUG_ON(nr_pages > 2);
> >> + if (*nr_pinned + nr_pages > NR_PINNED_PAGES_ON_STACK) {
> >
> > Is this a bug? Seems you will kzalloc() every time if *nr_pinned is
> > bigger than NR_PINNED_PAGES_ON_STACK, which will result in memory
> > leaking.
> >
> > I think the logic here is complex enough for us to introduce a
> > structure, like:
> >
> > struct cpu_opv_page_pinner {
> > int nr_pinned;
> > bool is_kmalloc;
> > struct page **pinned_pages;
> > };
> >
> > Thoughts?
>
> Good catch !
>
> How about the attached diff ? I'll fold it into the rseq/dev tree.
>
Looks good to me ;-)
Regards,
Boqun
> Thanks,
>
> Mathieu
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
> diff --git a/kernel/cpu_opv.c b/kernel/cpu_opv.c
> index 09754bbe6a4f..3d8fd66416a0 100644
> --- a/kernel/cpu_opv.c
> +++ b/kernel/cpu_opv.c
> @@ -46,6 +46,12 @@ union op_fn_data {
> #endif
> };
>
> +struct cpu_opv_pinned_pages {
> + struct page **pages;
> + size_t nr;
> + bool is_kmalloc;
> +};
> +
> typedef int (*op_fn_t)(union op_fn_data *data, uint64_t v, uint32_t len);
>
> static DEFINE_MUTEX(cpu_opv_offline_lock);
> @@ -217,8 +223,7 @@ static int cpu_op_check_pages(struct page **pages,
> }
>
> static int cpu_op_pin_pages(unsigned long addr, unsigned long len,
> - struct page ***pinned_pages_ptr, size_t *nr_pinned,
> - int write)
> + struct cpu_opv_pinned_pages *pin_pages, int write)
> {
> struct page *pages[2];
> int ret, nr_pages;
> @@ -227,15 +232,17 @@ static int cpu_op_pin_pages(unsigned long addr, unsigned long len,
> return 0;
> nr_pages = cpu_op_range_nr_pages(addr, len);
> BUG_ON(nr_pages > 2);
> - if (*nr_pinned + nr_pages > NR_PINNED_PAGES_ON_STACK) {
> + if (!pin_pages->is_kmalloc && pin_pages->nr + nr_pages
> + > NR_PINNED_PAGES_ON_STACK) {
> struct page **pinned_pages =
> kzalloc(CPU_OP_VEC_LEN_MAX * CPU_OP_MAX_PAGES
> * sizeof(struct page *), GFP_KERNEL);
> if (!pinned_pages)
> return -ENOMEM;
> - memcpy(pinned_pages, *pinned_pages_ptr,
> - *nr_pinned * sizeof(struct page *));
> - *pinned_pages_ptr = pinned_pages;
> + memcpy(pinned_pages, pin_pages->pages,
> + pin_pages->nr * sizeof(struct page *));
> + pin_pages->pages = pinned_pages;
> + pin_pages->is_kmalloc = true;
> }
> again:
> ret = get_user_pages_fast(addr, nr_pages, write, pages);
> @@ -257,9 +264,9 @@ static int cpu_op_pin_pages(unsigned long addr, unsigned long len,
> }
> if (ret)
> goto error;
> - (*pinned_pages_ptr)[(*nr_pinned)++] = pages[0];
> + pin_pages->pages[pin_pages->nr++] = pages[0];
> if (nr_pages > 1)
> - (*pinned_pages_ptr)[(*nr_pinned)++] = pages[1];
> + pin_pages->pages[pin_pages->nr++] = pages[1];
> return 0;
>
> error:
> @@ -270,7 +277,7 @@ static int cpu_op_pin_pages(unsigned long addr, unsigned long len,
> }
>
> static int cpu_opv_pin_pages(struct cpu_op *cpuop, int cpuopcnt,
> - struct page ***pinned_pages_ptr, size_t *nr_pinned)
> + struct cpu_opv_pinned_pages *pin_pages)
> {
> int ret, i;
> bool expect_fault = false;
> @@ -289,7 +296,7 @@ static int cpu_opv_pin_pages(struct cpu_op *cpuop, int cpuopcnt,
> goto error;
> ret = cpu_op_pin_pages(
> (unsigned long)op->u.compare_op.a,
> - op->len, pinned_pages_ptr, nr_pinned, 0);
> + op->len, pin_pages, 0);
> if (ret)
> goto error;
> ret = -EFAULT;
> @@ -299,7 +306,7 @@ static int cpu_opv_pin_pages(struct cpu_op *cpuop, int cpuopcnt,
> goto error;
> ret = cpu_op_pin_pages(
> (unsigned long)op->u.compare_op.b,
> - op->len, pinned_pages_ptr, nr_pinned, 0);
> + op->len, pin_pages, 0);
> if (ret)
> goto error;
> break;
> @@ -311,7 +318,7 @@ static int cpu_opv_pin_pages(struct cpu_op *cpuop, int cpuopcnt,
> goto error;
> ret = cpu_op_pin_pages(
> (unsigned long)op->u.memcpy_op.dst,
> - op->len, pinned_pages_ptr, nr_pinned, 1);
> + op->len, pin_pages, 1);
> if (ret)
> goto error;
> ret = -EFAULT;
> @@ -321,7 +328,7 @@ static int cpu_opv_pin_pages(struct cpu_op *cpuop, int cpuopcnt,
> goto error;
> ret = cpu_op_pin_pages(
> (unsigned long)op->u.memcpy_op.src,
> - op->len, pinned_pages_ptr, nr_pinned, 0);
> + op->len, pin_pages, 0);
> if (ret)
> goto error;
> break;
> @@ -333,7 +340,7 @@ static int cpu_opv_pin_pages(struct cpu_op *cpuop, int cpuopcnt,
> goto error;
> ret = cpu_op_pin_pages(
> (unsigned long)op->u.arithmetic_op.p,
> - op->len, pinned_pages_ptr, nr_pinned, 1);
> + op->len, pin_pages, 1);
> if (ret)
> goto error;
> break;
> @@ -347,7 +354,7 @@ static int cpu_opv_pin_pages(struct cpu_op *cpuop, int cpuopcnt,
> goto error;
> ret = cpu_op_pin_pages(
> (unsigned long)op->u.bitwise_op.p,
> - op->len, pinned_pages_ptr, nr_pinned, 1);
> + op->len, pin_pages, 1);
> if (ret)
> goto error;
> break;
> @@ -360,7 +367,7 @@ static int cpu_opv_pin_pages(struct cpu_op *cpuop, int cpuopcnt,
> goto error;
> ret = cpu_op_pin_pages(
> (unsigned long)op->u.shift_op.p,
> - op->len, pinned_pages_ptr, nr_pinned, 1);
> + op->len, pin_pages, 1);
> if (ret)
> goto error;
> break;
> @@ -373,9 +380,9 @@ static int cpu_opv_pin_pages(struct cpu_op *cpuop, int cpuopcnt,
> return 0;
>
> error:
> - for (i = 0; i < *nr_pinned; i++)
> - put_page((*pinned_pages_ptr)[i]);
> - *nr_pinned = 0;
> + for (i = 0; i < pin_pages->nr; i++)
> + put_page(pin_pages->pages[i]);
> + pin_pages->nr = 0;
> /*
> * If faulting access is expected, return EAGAIN to user-space.
> * It allows user-space to distinguish between a fault caused by
> @@ -923,9 +930,12 @@ SYSCALL_DEFINE4(cpu_opv, struct cpu_op __user *, ucpuopv, int, cpuopcnt,
> {
> struct cpu_op cpuopv[CPU_OP_VEC_LEN_MAX];
> struct page *pinned_pages_on_stack[NR_PINNED_PAGES_ON_STACK];
> - struct page **pinned_pages = pinned_pages_on_stack;
> + struct cpu_opv_pinned_pages pin_pages = {
> + .pages = pinned_pages_on_stack,
> + .nr = 0,
> + .is_kmalloc = false,
> + };
> int ret, i;
> - size_t nr_pinned = 0;
>
> if (unlikely(flags))
> return -EINVAL;
> @@ -938,15 +948,14 @@ SYSCALL_DEFINE4(cpu_opv, struct cpu_op __user *, ucpuopv, int, cpuopcnt,
> ret = cpu_opv_check(cpuopv, cpuopcnt);
> if (ret)
> return ret;
> - ret = cpu_opv_pin_pages(cpuopv, cpuopcnt,
> - &pinned_pages, &nr_pinned);
> + ret = cpu_opv_pin_pages(cpuopv, cpuopcnt, &pin_pages);
> if (ret)
> goto end;
> ret = do_cpu_opv(cpuopv, cpuopcnt, cpu);
> - for (i = 0; i < nr_pinned; i++)
> - put_page(pinned_pages[i]);
> + for (i = 0; i < pin_pages.nr; i++)
> + put_page(pin_pages.pages[i]);
> end:
> - if (pinned_pages != pinned_pages_on_stack)
> - kfree(pinned_pages);
> + if (pin_pages.is_kmalloc)
> + kfree(pin_pages.pages);
> return ret;
> }
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