cxl: Change contexts_lock to a mutex to fix sleep while atomic bug

We had a known sleep while atomic bug if a CXL device was forcefully
unbound while it was in use. This could occur as a result of EEH, or
manually induced with something like this while the device was in use:

echo 0000:01:00.0 > /sys/bus/pci/drivers/cxl-pci/unbind

The issue was that in this code path we iterated over each context and
forcefully detached it with the contexts_lock spin lock held, however
the detach also needed to take the spu_mutex, and call schedule.

This patch changes the contexts_lock to a mutex so that we are not in
atomic context while doing the detach, thereby avoiding the sleep while
atomic.

Also delete the related TODO comment, which suggested an alternate
solution which turned out to not be workable.

Cc: stable@vger.kernel.org
Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/drivers/misc/cxl/context.c b/drivers/misc/cxl/context.c
index cca47210913524d3c57fb118894c97d0c18552f0..4aa31a3fb4482267bb5188e292df8cddc340a0b4 100644 (file)
--- a/drivers/misc/cxl/context.c
+++ b/drivers/misc/cxl/context.c
@@ -82,12 +82,12 @@ int cxl_context_init(struct cxl_context *ctx, struct cxl_afu *afu, bool master)
         * Allocating IDR! We better make sure everything's setup that
         * dereferences from it.
         */
+       mutex_lock(&afu->contexts_lock);
        idr_preload(GFP_KERNEL);
-       spin_lock(&afu->contexts_lock);
        i = idr_alloc(&ctx->afu->contexts_idr, ctx, 0,
                      ctx->afu->num_procs, GFP_NOWAIT);
-       spin_unlock(&afu->contexts_lock);
        idr_preload_end();
+       mutex_unlock(&afu->contexts_lock);
        if (i < 0)
                return i;
 
@@ -168,21 +168,22 @@ void cxl_context_detach_all(struct cxl_afu *afu)
        struct cxl_context *ctx;
        int tmp;
 
-       rcu_read_lock();
-       idr_for_each_entry(&afu->contexts_idr, ctx, tmp)
+       mutex_lock(&afu->contexts_lock);
+       idr_for_each_entry(&afu->contexts_idr, ctx, tmp) {
                /*
                 * Anything done in here needs to be setup before the IDR is
                 * created and torn down after the IDR removed
                 */
                __detach_context(ctx);
-       rcu_read_unlock();
+       }
+       mutex_unlock(&afu->contexts_lock);
 }
 
 void cxl_context_free(struct cxl_context *ctx)
 {
-       spin_lock(&ctx->afu->contexts_lock);
+       mutex_lock(&ctx->afu->contexts_lock);
        idr_remove(&ctx->afu->contexts_idr, ctx->pe);
-       spin_unlock(&ctx->afu->contexts_lock);
+       mutex_unlock(&ctx->afu->contexts_lock);
        synchronize_rcu();
 
        free_page((u64)ctx->sstp);

diff --git a/drivers/misc/cxl/cxl.h b/drivers/misc/cxl/cxl.h
index b5b6bda44a009c1732ef7832a9884ddc556ac127..7c05239359df6ba9bc1bc03d50cb2d5142b531dd 100644 (file)
--- a/drivers/misc/cxl/cxl.h
+++ b/drivers/misc/cxl/cxl.h
@@ -351,7 +351,7 @@ struct cxl_afu {
        struct device *chardev_s, *chardev_m, *chardev_d;
        struct idr contexts_idr;
        struct dentry *debugfs;
-       spinlock_t contexts_lock;
+       struct mutex contexts_lock;
        struct mutex spa_mutex;
        spinlock_t afu_cntl_lock;
 

diff --git a/drivers/misc/cxl/native.c b/drivers/misc/cxl/native.c
index 9a5a442269a870a7e22f699b77c5e041212b6bf1..1001cf49af94265cc2c74abd5979dee2c1bd6095 100644 (file)
--- a/drivers/misc/cxl/native.c
+++ b/drivers/misc/cxl/native.c
@@ -610,13 +610,6 @@ static inline int detach_process_native_dedicated(struct cxl_context *ctx)
        return 0;
 }
 
-/*
- * TODO: handle case when this is called inside a rcu_read_lock() which may
- * happen when we unbind the driver (ie. cxl_context_detach_all()) .  Terminate
- * & remove use a mutex lock and schedule which will not good with lock held.
- * May need to write do_process_element_cmd() that handles outstanding page
- * faults synchronously.
- */
 static inline int detach_process_native_afu_directed(struct cxl_context *ctx)
 {
        if (!ctx->pe_inserted)

diff --git a/drivers/misc/cxl/pci.c b/drivers/misc/cxl/pci.c
index 10c98ab7f46e1c7fb6a796d4dde06d194fe97204..0f2cc9f8b4dbcd456bbccfab21bf3124f660e6be 100644 (file)
--- a/drivers/misc/cxl/pci.c
+++ b/drivers/misc/cxl/pci.c
@@ -502,7 +502,7 @@ static struct cxl_afu *cxl_alloc_afu(struct cxl *adapter, int slice)
        afu->dev.release = cxl_release_afu;
        afu->slice = slice;
        idr_init(&afu->contexts_idr);
-       spin_lock_init(&afu->contexts_lock);
+       mutex_init(&afu->contexts_lock);
        spin_lock_init(&afu->afu_cntl_lock);
        mutex_init(&afu->spa_mutex);
 

diff --git a/drivers/misc/cxl/sysfs.c b/drivers/misc/cxl/sysfs.c
index ce7ec06d87d13d6f0cadce4d254a715e6d2810fc..461bdbd5d48317fa941ac002aa1f014761336f9a 100644 (file)
--- a/drivers/misc/cxl/sysfs.c
+++ b/drivers/misc/cxl/sysfs.c
@@ -121,7 +121,7 @@ static ssize_t reset_store_afu(struct device *device,
        int rc;
 
        /* Not safe to reset if it is currently in use */
-       spin_lock(&afu->contexts_lock);
+       mutex_lock(&afu->contexts_lock);
        if (!idr_is_empty(&afu->contexts_idr)) {
                rc = -EBUSY;
                goto err;
@@ -132,7 +132,7 @@ static ssize_t reset_store_afu(struct device *device,
 
        rc = count;
 err:
-       spin_unlock(&afu->contexts_lock);
+       mutex_unlock(&afu->contexts_lock);
        return rc;
 }
 
@@ -247,7 +247,7 @@ static ssize_t mode_store(struct device *device, struct device_attribute *attr,
        int rc = -EBUSY;
 
        /* can't change this if we have a user */
-       spin_lock(&afu->contexts_lock);
+       mutex_lock(&afu->contexts_lock);
        if (!idr_is_empty(&afu->contexts_idr))
                goto err;
 
@@ -271,7 +271,7 @@ static ssize_t mode_store(struct device *device, struct device_attribute *attr,
        afu->current_mode = 0;
        afu->num_procs = 0;
 
-       spin_unlock(&afu->contexts_lock);
+       mutex_unlock(&afu->contexts_lock);
 
        if ((rc = _cxl_afu_deactivate_mode(afu, old_mode)))
                return rc;
@@ -280,7 +280,7 @@ static ssize_t mode_store(struct device *device, struct device_attribute *attr,
 
        return count;
 err:
-       spin_unlock(&afu->contexts_lock);
+       mutex_unlock(&afu->contexts_lock);
        return rc;
 }