| Message ID | 20240903-fix_cxld-v1-1-61acba7198ae@quicinc.com |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | cxl/region: Fix logic for finding a free cxl decoder | expand |
On Tue, Sep 03, 2024 at 08:41:44PM +0800, Zijun Hu wrote: > From: Zijun Hu <quic_zijuhu@quicinc.com> > > match_free_decoder()'s logic for finding a free cxl decoder depends on > a prerequisite that all child decoders are sorted by ID in ascending order > but the prerequisite may not be guaranteed, fix by finding a free cxl > decoder with minimal ID. After reading the 'Closes' tag below I have a better understanding of why you may be doing this, but I don't want to have to jump to that Link. Can you describe here examples of when the ordered allocation may not be guaranteed, and the impact when that happens. This includes a change to device_for_each_child() which I see mentioned in the Closes tag discussion too. Is that required for this fix? It's feeling like the fix and api update are comingled. Please clarify. Thanks, Alison > > Fixes: 384e624bb211 ("cxl/region: Attach endpoint decoders") > Closes: https://lore.kernel.org/all/cdfc6f98-1aa0-4cb5-bd7d-93256552c39b@icloud.com/ > Cc: stable@vger.kernel.org > Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com> > --- > drivers/cxl/core/region.c | 27 ++++++++++++++++----------- > 1 file changed, 16 insertions(+), 11 deletions(-) > > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c > index 21ad5f242875..b9607b4fc40b 100644 > --- a/drivers/cxl/core/region.c > +++ b/drivers/cxl/core/region.c > @@ -797,21 +797,26 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos) > static int match_free_decoder(struct device *dev, void *data) > { > struct cxl_decoder *cxld; > - int *id = data; > + struct cxl_decoder *target_cxld; > + struct device **target_device = data; > > if (!is_switch_decoder(dev)) > return 0; > > cxld = to_cxl_decoder(dev); > - > - /* enforce ordered allocation */ > - if (cxld->id != *id) > + if (cxld->region) > return 0; > > - if (!cxld->region) > - return 1; > - > - (*id)++; > + if (!*target_device) { > + *target_device = get_device(dev); > + return 0; > + } > + /* enforce ordered allocation */ > + target_cxld = to_cxl_decoder(*target_device); > + if (cxld->id < target_cxld->id) { > + put_device(*target_device); > + *target_device = get_device(dev); > + } > > return 0; > } > @@ -839,8 +844,7 @@ cxl_region_find_decoder(struct cxl_port *port, > struct cxl_endpoint_decoder *cxled, > struct cxl_region *cxlr) > { > - struct device *dev; > - int id = 0; > + struct device *dev = NULL; > > if (port == cxled_to_port(cxled)) > return &cxled->cxld; > @@ -849,7 +853,8 @@ cxl_region_find_decoder(struct cxl_port *port, > dev = device_find_child(&port->dev, &cxlr->params, > match_auto_decoder); > else > - dev = device_find_child(&port->dev, &id, match_free_decoder); > + /* Need to put_device(@dev) after use */ > + device_for_each_child(&port->dev, &dev, match_free_decoder); > if (!dev) > return NULL; > /* > > --- > base-commit: 67784a74e258a467225f0e68335df77acd67b7ab > change-id: 20240903-fix_cxld-4f6575a90619 > > Best regards, > -- > Zijun Hu <quic_zijuhu@quicinc.com> >
On 2024/9/4 04:14, Alison Schofield wrote: > On Tue, Sep 03, 2024 at 08:41:44PM +0800, Zijun Hu wrote: >> From: Zijun Hu <quic_zijuhu@quicinc.com> >> >> match_free_decoder()'s logic for finding a free cxl decoder depends on >> a prerequisite that all child decoders are sorted by ID in ascending order >> but the prerequisite may not be guaranteed, fix by finding a free cxl >> decoder with minimal ID. > > After reading the 'Closes' tag below I have a better understanding of > why you may be doing this, but I don't want to have to jump to that > Link. Can you describe here examples of when the ordered allocation > may not be guaranteed, and the impact when that happens. > thank you for code review. let me try to do it. > This includes a change to device_for_each_child() which I see mentioned > in the Closes tag discussion too. Is that required for this fix? > yes, device_for_each_child() is better than device_find_child() to correct logic for finding a free cxl decoder. > It's feeling like the fix and api update are comingled. Please clarify. > actually, there are two concerns as shown below: concern A: device_find_child() modifies caller's match data. concern B: weird logic for finding a free cxl decoder this patch focuses on concern B, and it also solve concern A in passing. the following exclusive patch only solves concern A. https://lore.kernel.org/all/20240905-const_dfc_prepare-v4-1-4180e1d5a244@quicinc.com/ either will solve concern A i care about. > Thanks, > Alison > >>
diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c index 21ad5f242875..b9607b4fc40b 100644 --- a/drivers/cxl/core/region.c +++ b/drivers/cxl/core/region.c @@ -797,21 +797,26 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos) static int match_free_decoder(struct device *dev, void *data) { struct cxl_decoder *cxld; - int *id = data; + struct cxl_decoder *target_cxld; + struct device **target_device = data; if (!is_switch_decoder(dev)) return 0; cxld = to_cxl_decoder(dev); - - /* enforce ordered allocation */ - if (cxld->id != *id) + if (cxld->region) return 0; - if (!cxld->region) - return 1; - - (*id)++; + if (!*target_device) { + *target_device = get_device(dev); + return 0; + } + /* enforce ordered allocation */ + target_cxld = to_cxl_decoder(*target_device); + if (cxld->id < target_cxld->id) { + put_device(*target_device); + *target_device = get_device(dev); + } return 0; } @@ -839,8 +844,7 @@ cxl_region_find_decoder(struct cxl_port *port, struct cxl_endpoint_decoder *cxled, struct cxl_region *cxlr) { - struct device *dev; - int id = 0; + struct device *dev = NULL; if (port == cxled_to_port(cxled)) return &cxled->cxld; @@ -849,7 +853,8 @@ cxl_region_find_decoder(struct cxl_port *port, dev = device_find_child(&port->dev, &cxlr->params, match_auto_decoder); else - dev = device_find_child(&port->dev, &id, match_free_decoder); + /* Need to put_device(@dev) after use */ + device_for_each_child(&port->dev, &dev, match_free_decoder); if (!dev) return NULL; /*