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cxl: Prevent adapter reset if an active context exists

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This patch prevents resetting the cxl adapter via sysfs in presence of
one or more active cxl_context on it. This protects against an
unrecoverable error caused by PSL owning a dirty cache line even after
reset and host tries to touch the same cache line. In case a force reset
of the card is required irrespective of any active contexts, the int
value -1 can be stored in the 'reset' sysfs attribute of the card.

The patch introduces a new atomic_t member named contexts_num inside
struct cxl that holds the number of active context attached to the card
, which is checked against '0' before proceeding with the reset. To
prevent against a race condition where a context is activated just after
reset check is performed, the contexts_num is atomically set to '-1'
after reset-check to indicate that no more contexts can be activated on
the card anymore.

Before activating a context we atomically test if contexts_num is
non-negative and if so, increment its value by one. In case the value of
contexts_num is negative then it indicates that the card is about to be
reset and context activation is error-ed out at that point.

Fixes: 62fa19d4b4 ("cxl: Add ability to reset the card")
Cc: stable@vger.kernel.org # v4.0+
Acked-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Vaibhav Jain
2016-10-14 15:08:36 +05:30
committed by Michael Ellerman
parent 65bc3ece84
commit 70b565bbdb
9 changed files with 121 additions and 7 deletions
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42
drivers/misc/cxl/main.c
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@@ -243,8 +243,10 @@ struct cxl *cxl_alloc_adapter(void)
if (dev_set_name(&adapter->dev, "card%i", adapter->adapter_num))
goto err2;
return adapter;
/* start with context lock taken */
atomic_set(&adapter->contexts_num, -1);
return adapter;
err2:
cxl_remove_adapter_nr(adapter);
err1:
@@ -286,6 +288,44 @@ int cxl_afu_select_best_mode(struct cxl_afu *afu)
return 0;
}
int cxl_adapter_context_get(struct cxl *adapter)
{
int rc;
rc = atomic_inc_unless_negative(&adapter->contexts_num);
return rc >= 0 ? 0 : -EBUSY;
}
void cxl_adapter_context_put(struct cxl *adapter)
{
atomic_dec_if_positive(&adapter->contexts_num);
}
int cxl_adapter_context_lock(struct cxl *adapter)
{
int rc;
/* no active contexts -> contexts_num == 0 */
rc = atomic_cmpxchg(&adapter->contexts_num, 0, -1);
return rc ? -EBUSY : 0;
}
void cxl_adapter_context_unlock(struct cxl *adapter)
{
int val = atomic_cmpxchg(&adapter->contexts_num, -1, 0);
/*
* contexts lock taken -> contexts_num == -1
* If not true then show a warning and force reset the lock.
* This will happen when context_unlock was requested without
* doing a context_lock.
*/
if (val != -1) {
atomic_set(&adapter->contexts_num, 0);
WARN(1, "Adapter context unlocked with %d active contexts",
val);
}
}
static int __init init_cxl(void)
{
int rc = 0;