Henrique de Moraes Holschuh
2017-04-10T23:49:40Z

Author: Henrique de Moraes Holschuh <hmh@debian.org>
Date: Wed Feb 1 20:42:02 2017 -0200

sd: wait for slow devices on shutdown path

Wait 1s during suspend/shutdown for the device to settle after
we issue the STOP command.

Otherwise we race ATA SSDs to powerdown, possibly causing damage to
FLASH/data and even bricking the device.

This is an experimental patch, there are likely better ways of doing
this that don't punish non-SSDs.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 4e08d1cd..3c6d5d3 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -3230,6 +3230,38 @@ static int sd_start_stop_device(struct scsi_disk *sdkp, int start)
res = 0;
}

+ /*
+ * Wait for slow devices that signal they have fully entered
+ * the stopped state before they actully did it.
+ *
+ * This behavior is apparently allowed per-spec for ATA
+ * devices, and our SAT layer does not account for it.
+ * Thus, on return, the device might still be in the process
+ * of entering STANDBY state.
+ *
+ * Worse, apparently the ATA spec also says the unit should
+ * return that it is already in STANDBY state *while still
+ * entering that state*.
+ *
+ * SSDs absolutely depend on receiving a STANDBY IMMEDIATE
+ * command prior to power off for a clean shutdown (and
+ * likely we don't want to send them *anything else* in-
+ * between either, to be on the safe side).
+ *
+ * As things stand, we are racing the SSD's firmware. If it
+ * finishes first, nothing bad happens. If it doesn't, we
+ * cut power while it is still saving metadata, and not only
+ * this will cause extra FLASH wear (and maybe even damage
+ * some cells), it also has a non-zero chance of bricking the
+ * SSD.
+ *
+ * Issue reported on Intel, Crucial and Micron SSDs.
+ * Issue can be detected by S.M.A.R.T. signaling unexpected
+ * power cuts.
+ */
+ if (!res && !start)
+ msleep(1000);
+
/* SCSI error codes must not go to the generic layer */
if (res)
return -EIO;

--
Henrique Holschuh