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Message-ID: <20250623113208.0000768c@huawei.com>
Date: Mon, 23 Jun 2025 11:32:08 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Dan Williams <dan.j.williams@...el.com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>, David Lechner
<dlechner@...libre.com>, Peter Zijlstra <peterz@...radead.org>, "Linus
Torvalds" <torvalds@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>,
"Fabio M. De Francesco" <fabio.maria.de.francesco@...ux.intel.com>, Davidlohr
Bueso <dave@...olabs.net>, Dave Jiang <dave.jiang@...el.com>, Alison
Schofield <alison.schofield@...el.com>, Vishal Verma
<vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, Shiju Jose
<shiju.jose@...wei.com>
Subject: Re: [PATCH v2 8/8] cxl: Convert to ACQUIRE() for conditional rwsem
locking
On Wed, 18 Jun 2025 22:04:16 -0700
Dan Williams <dan.j.williams@...el.com> wrote:
> Use ACQUIRE() to cleanup conditional locking paths in the CXL driver
> The ACQUIRE() macro and its associated ACQUIRE_ERR() helpers, like
> scoped_cond_guard(), arrange for scoped-based conditional locking. Unlike
> scoped_cond_guard(), these macros arrange for an ERR_PTR() to be retrieved
> representing the state of the conditional lock.
>
> The goal of this conversion is to complete the removal of all explicit
> unlock calls in the subsystem. I.e. the methods to acquire a lock are
> solely via guard(), scoped_guard() (for limited cases), or ACQUIRE(). All
> unlock is implicit / scope-based. In order to make sure all lock sites are
> converted, the existing rwsem's are consolidated and renamed in 'struct
> cxl_rwsem'. While that makes the patch noisier it gives a clean cut-off
> between old-world (explicit unlock allowed), and new world (explicit unlock
> deleted).
>
> Cc: David Lechner <dlechner@...libre.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: "Fabio M. De Francesco" <fabio.maria.de.francesco@...ux.intel.com>
> Cc: Davidlohr Bueso <dave@...olabs.net>
> Cc: Jonathan Cameron <jonathan.cameron@...wei.com>
> Cc: Dave Jiang <dave.jiang@...el.com>
> Cc: Alison Schofield <alison.schofield@...el.com>
> Cc: Vishal Verma <vishal.l.verma@...el.com>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: Shiju Jose <shiju.jose@...wei.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
A few comments inline.
> index 010964aa5489..a2ba19151d4f 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> static DEVICE_ATTR_RW(interleave_ways);
> @@ -561,15 +537,11 @@ static ssize_t interleave_granularity_show(struct device *dev,
> {
> struct cxl_region *cxlr = to_cxl_region(dev);
> struct cxl_region_params *p = &cxlr->params;
> - ssize_t rc;
> -
> - rc = down_read_interruptible(&cxl_region_rwsem);
> - if (rc)
> - return rc;
> - rc = sysfs_emit(buf, "%d\n", p->interleave_granularity);
> - up_read(&cxl_region_rwsem);
>
> - return rc;
> + ACQUIRE(rwsem_read_intr, rwsem)(&cxl_rwsem.region);
> + if (ACQUIRE_ERR(rwsem_read_intr, &rwsem))
> + return ACQUIRE_ERR(rwsem_read_intr, &rwsem);
Local variable?
> + return sysfs_emit(buf, "%d\n", p->interleave_granularity);
> }
> @@ -2212,19 +2167,19 @@ static int attach_target(struct cxl_region *cxlr,
> struct cxl_endpoint_decoder *cxled, int pos,
> unsigned int state)
> {
> - int rc = 0;
> -
> - if (state == TASK_INTERRUPTIBLE)
> - rc = down_write_killable(&cxl_region_rwsem);
> - else
> - down_write(&cxl_region_rwsem);
> - if (rc)
> - return rc;
> + int rc;
>
> - down_read(&cxl_dpa_rwsem);
> - rc = cxl_region_attach(cxlr, cxled, pos);
> - up_read(&cxl_dpa_rwsem);
> - up_write(&cxl_region_rwsem);
> + if (state == TASK_INTERRUPTIBLE) {
> + ACQUIRE(rwsem_write_kill, rwsem)(&cxl_rwsem.region);
> + if ((rc = ACQUIRE_ERR(rwsem_write_kill, &rwsem)) == 0) {
I'd lift the warning print to a wrapper function so that you can
return early in error case and avoid this rather messy line.
e.g.
static int do_attach_target(struct cxl_region *cxlr,
struct cxl_endpoint_decoder *cxled, int pos,
unsigned int state)
if (state == TASK_INTERRUPTIBLE) {
ACQUIRE(rwsem_write_kill, rwsem)(&cxl_rwsem.region);
rc = ACQUIRE_ERR(rwsem_write_kill, &rwsem);
if (rc)
return rc;
guard(rwsem_read)(&cxl_rwsem.dpa);
return cxl_region_attach(cxlr, cxled, pos);
}
guard(rwsem_write)(&cxl_rwsem.region);
guard(rwsem_read)(&cxl_rwsem.dpa);
return cxl_region_attach(cxlr, cxled, pos);
}
static int attach_target(struct cxl_region *cxlr,
struct cxl_endpoint_decoder *cxled, int pos,
unsigned int state)
{
int rc = do_attach_target(cxlr, cxled, pos, state);
if (rc)
dev_warn();
return rc;
}
> + guard(rwsem_read)(&cxl_rwsem.dpa);
> + rc = cxl_region_attach(cxlr, cxled, pos);
> + }
> + } else {
> + guard(rwsem_write)(&cxl_rwsem.region);
> + guard(rwsem_read)(&cxl_rwsem.dpa);
> + rc = cxl_region_attach(cxlr, cxled, pos);
> + }
>
> if (rc)
> dev_warn(cxled->cxld.dev.parent,
> @@ -3569,30 +3520,23 @@ static int cxl_region_can_probe(struct cxl_region *cxlr)
> struct cxl_region_params *p = &cxlr->params;
> int rc;
>
> - rc = down_read_interruptible(&cxl_region_rwsem);
> - if (rc) {
> + ACQUIRE(rwsem_read_intr, rwsem)(&cxl_rwsem.region);
Similar to earlier - I'd do this next bit in two lines for slightly
better readability. Same for the other cases. I don't care that strongly
though.
> + if ((rc = ACQUIRE_ERR(rwsem_read_intr, &rwsem))) {
> dev_dbg(&cxlr->dev, "probe interrupted\n");
> return rc;
> }
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