Messages in this thread Patch in this message | | | Date | Wed, 7 Dec 2022 13:39:58 -0800 | From | Dan Williams <> | Subject | Re: [PATCH v3 2/6] cxl/mbox: Add GET_POISON_LIST mailbox command |
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Alison Schofield wrote: > On Tue, Dec 06, 2022 at 06:41:34PM -0800, Dan Williams wrote: > > alison.schofield@ wrote: [..] > > > +int cxl_mem_get_poison(struct cxl_memdev *cxlmd, u64 offset, u64 len, > > > + struct cxl_region *cxlr) > > > +{ > > > + struct cxl_dev_state *cxlds = cxlmd->cxlds; > > > + const char *memdev_name = dev_name(&cxlmd->dev); > > > + const char *pcidev_name = dev_name(cxlds->dev); > > > + struct cxl_mbox_poison_payload_out *po; > > > + struct cxl_mbox_poison_payload_in pi; > > > + int nr_records = 0; > > > + int rc; > > > + > > > + po = kvmalloc(cxlds->payload_size, GFP_KERNEL); > > > + if (!po) > > > + return -ENOMEM; > > > + > > > + pi.offset = cpu_to_le64(offset); > > > + pi.length = cpu_to_le64(len); > > > + > > > + rc = mutex_lock_interruptible(&cxlds->poison_list_mutex); > > > > So I do not know what this mutex is protecting if there is an allocation > > per cxl_mem_get_poison() invocation. Although I suspect that's somewhat > > wasteful. Just allocate one buffer at the beginning of time and then use > > the lock to protect that buffer. > > Intent was a single lock on the device to protect the state of the > poison list retrieval - do not allow > 1 reader. With > 1 reader > software may not know if it retrieved the complete list. > > I'm not understanding about protecting a buffer, instead of protecting > the state. Here I try to protect the state.
Ah, sorry I read cxlds->poison_list_mutex and assumed it was serializing access to the buffer, not a state machine. I do think it would be worthwhile to make this a self contained structure with its own kdoc to explain what is going on, something like:
diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h index ab138004f644..02697d1d951c 100644 --- a/drivers/cxl/cxlmem.h +++ b/drivers/cxl/cxlmem.h @@ -193,6 +193,19 @@ struct cxl_endpoint_dvsec_info { struct range dvsec_range[2]; }; +/** + * struct cxl_poison_state - summary + * @payload: ... + * @lock: ... + * + * A bit more description of why state needs to be held over successive + * mbox commands... + */ +struct cxl_poison_state { + void *payload; + struct mutex lock; +}; + /** * struct cxl_dev_state - The driver device state * @@ -210,6 +223,7 @@ struct cxl_endpoint_dvsec_info { * @lsa_size: Size of Label Storage Area * (CXL 2.0 8.2.9.5.1.1 Identify Memory Device) * @mbox_mutex: Mutex to synchronize mailbox access. + * @poison: Poison list retrieval and tracing * @firmware_version: Firmware version for the memory device. * @enabled_cmds: Hardware commands found enabled in CEL. * @exclusive_cmds: Commands that are kernel-internal only @@ -244,6 +258,7 @@ struct cxl_dev_state { size_t payload_size; size_t lsa_size; struct mutex mbox_mutex; /* Protects device mailbox and firmware */ + struct cxl_poison_state poison; char firmware_version[0x10]; DECLARE_BITMAP(enabled_cmds, CXL_MEM_COMMAND_ID_MAX); DECLARE_BITMAP(exclusive_cmds, CXL_MEM_COMMAND_ID_MAX);
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