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authorMatthew R. Ochs <mrochs@linux.vnet.ibm.com>2015-10-21 15:15:52 -0500
committerJames Bottomley <JBottomley@Odin.com>2015-10-30 17:22:11 +0900
commitaacb4ff69eea4ac47a7389f90ea7a896abbe92f5 (patch)
tree8318e4ff5a29e309f91786c7beb386cb97524d5d /drivers
parentfa3f2c6eb1eb69a9023d648c5bafbf4f062ab84d (diff)
cxlflash: Fix to avoid potential deadlock on EEH
Ioctl threads that use scsi_execute() can run for an excessive amount of time due to the fact that they have lengthy timeouts and retry logic built in. Under normal operation this is not an issue. However, once EEH enters the picture, a long execution time coupled with the possibility that a timeout can trigger entry to the driver via registered reset callbacks becomes a liability. In particular, a deadlock can occur when an EEH event is encountered while in running in scsi_execute(). As part of the recovery, the EEH handler drains all currently running ioctls, waiting until they have completed before proceeding with a reset. As the scsi_execute()'s are situated on the ioctl path, the EEH handler will wait until they (and the remainder of the ioctl handler they're associated with) have completed. Normally this would not be much of an issue aside from the longer recovery period. Unfortunately, the scsi_execute() triggers a reset when it times out. The reset handler will see that the device is already being reset and wait until that reset completed. This creates a condition where the EEH handler becomes stuck, infinitely waiting for the ioctl thread to complete. To avoid this behavior, temporarily unmark the scsi_execute() threads as an ioctl thread by releasing the ioctl read semaphore. This allows the EEH handler to proceed with a recovery while the thread is still running. Once the scsi_execute() returns, the ioctl read semaphore is reacquired and the adapter state is rechecked in case it changed while inside of scsi_execute(). The state check will wait if the adapter is still being recovered or returns a failure if the recovery failed. In the event that the adapter reset failed, the failure is simply returned as the ioctl would be unable to continue. Reported-by: Brian King <brking@linux.vnet.ibm.com> Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com> Signed-off-by: Manoj N. Kumar <manoj@linux.vnet.ibm.com> Reviewed-by: Brian King <brking@linux.vnet.ibm.com> Reviewed-by: Daniel Axtens <dja@axtens.net> Reviewed-by: Tomas Henzl <thenzl@redhat.com> Signed-off-by: James Bottomley <JBottomley@Odin.com>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/scsi/cxlflash/superpipe.c30
-rw-r--r--drivers/scsi/cxlflash/superpipe.h2
-rw-r--r--drivers/scsi/cxlflash/vlun.c29
3 files changed, 60 insertions, 1 deletions
diff --git a/drivers/scsi/cxlflash/superpipe.c b/drivers/scsi/cxlflash/superpipe.c
index 34acb587d730..18a5e11aac3a 100644
--- a/drivers/scsi/cxlflash/superpipe.c
+++ b/drivers/scsi/cxlflash/superpipe.c
@@ -283,6 +283,24 @@ out:
* @sdev: SCSI device associated with LUN.
* @lli: LUN destined for capacity request.
*
+ * The READ_CAP16 can take quite a while to complete. Should an EEH occur while
+ * in scsi_execute(), the EEH handler will attempt to recover. As part of the
+ * recovery, the handler drains all currently running ioctls, waiting until they
+ * have completed before proceeding with a reset. As this routine is used on the
+ * ioctl path, this can create a condition where the EEH handler becomes stuck,
+ * infinitely waiting for this ioctl thread. To avoid this behavior, temporarily
+ * unmark this thread as an ioctl thread by releasing the ioctl read semaphore.
+ * This will allow the EEH handler to proceed with a recovery while this thread
+ * is still running. Once the scsi_execute() returns, reacquire the ioctl read
+ * semaphore and check the adapter state in case it changed while inside of
+ * scsi_execute(). The state check will wait if the adapter is still being
+ * recovered or return a failure if the recovery failed. In the event that the
+ * adapter reset failed, simply return the failure as the ioctl would be unable
+ * to continue.
+ *
+ * Note that the above puts a requirement on this routine to only be called on
+ * an ioctl thread.
+ *
* Return: 0 on success, -errno on failure
*/
static int read_cap16(struct scsi_device *sdev, struct llun_info *lli)
@@ -314,8 +332,18 @@ retry:
dev_dbg(dev, "%s: %ssending cmd(0x%x)\n", __func__,
retry_cnt ? "re" : "", scsi_cmd[0]);
+ /* Drop the ioctl read semahpore across lengthy call */
+ up_read(&cfg->ioctl_rwsem);
result = scsi_execute(sdev, scsi_cmd, DMA_FROM_DEVICE, cmd_buf,
CMD_BUFSIZE, sense_buf, to, CMD_RETRIES, 0, NULL);
+ down_read(&cfg->ioctl_rwsem);
+ rc = check_state(cfg);
+ if (rc) {
+ dev_err(dev, "%s: Failed state! result=0x08%X\n",
+ __func__, result);
+ rc = -ENODEV;
+ goto out;
+ }
if (driver_byte(result) == DRIVER_SENSE) {
result &= ~(0xFF<<24); /* DRIVER_SENSE is not an error */
@@ -1221,7 +1249,7 @@ static const struct file_operations null_fops = {
*
* Return: 0 on success, -errno on failure
*/
-static int check_state(struct cxlflash_cfg *cfg)
+int check_state(struct cxlflash_cfg *cfg)
{
struct device *dev = &cfg->dev->dev;
int rc = 0;
diff --git a/drivers/scsi/cxlflash/superpipe.h b/drivers/scsi/cxlflash/superpipe.h
index 7df88eeea9c0..06a805ab1439 100644
--- a/drivers/scsi/cxlflash/superpipe.h
+++ b/drivers/scsi/cxlflash/superpipe.h
@@ -147,4 +147,6 @@ void cxlflash_ba_terminate(struct ba_lun *);
int cxlflash_manage_lun(struct scsi_device *, struct dk_cxlflash_manage_lun *);
+int check_state(struct cxlflash_cfg *);
+
#endif /* ifndef _CXLFLASH_SUPERPIPE_H */
diff --git a/drivers/scsi/cxlflash/vlun.c b/drivers/scsi/cxlflash/vlun.c
index b0eaf557cc2f..a53f583e2d7b 100644
--- a/drivers/scsi/cxlflash/vlun.c
+++ b/drivers/scsi/cxlflash/vlun.c
@@ -400,6 +400,24 @@ static int init_vlun(struct llun_info *lli)
* @lba: Logical block address to start write same.
* @nblks: Number of logical blocks to write same.
*
+ * The SCSI WRITE_SAME16 can take quite a while to complete. Should an EEH occur
+ * while in scsi_execute(), the EEH handler will attempt to recover. As part of
+ * the recovery, the handler drains all currently running ioctls, waiting until
+ * they have completed before proceeding with a reset. As this routine is used
+ * on the ioctl path, this can create a condition where the EEH handler becomes
+ * stuck, infinitely waiting for this ioctl thread. To avoid this behavior,
+ * temporarily unmark this thread as an ioctl thread by releasing the ioctl read
+ * semaphore. This will allow the EEH handler to proceed with a recovery while
+ * this thread is still running. Once the scsi_execute() returns, reacquire the
+ * ioctl read semaphore and check the adapter state in case it changed while
+ * inside of scsi_execute(). The state check will wait if the adapter is still
+ * being recovered or return a failure if the recovery failed. In the event that
+ * the adapter reset failed, simply return the failure as the ioctl would be
+ * unable to continue.
+ *
+ * Note that the above puts a requirement on this routine to only be called on
+ * an ioctl thread.
+ *
* Return: 0 on success, -errno on failure
*/
static int write_same16(struct scsi_device *sdev,
@@ -433,9 +451,20 @@ static int write_same16(struct scsi_device *sdev,
put_unaligned_be32(ws_limit < left ? ws_limit : left,
&scsi_cmd[10]);
+ /* Drop the ioctl read semahpore across lengthy call */
+ up_read(&cfg->ioctl_rwsem);
result = scsi_execute(sdev, scsi_cmd, DMA_TO_DEVICE, cmd_buf,
CMD_BUFSIZE, sense_buf, to, CMD_RETRIES,
0, NULL);
+ down_read(&cfg->ioctl_rwsem);
+ rc = check_state(cfg);
+ if (rc) {
+ dev_err(dev, "%s: Failed state! result=0x08%X\n",
+ __func__, result);
+ rc = -ENODEV;
+ goto out;
+ }
+
if (result) {
dev_err_ratelimited(dev, "%s: command failed for "
"offset %lld result=0x%x\n",