ata: fixes kernel crash while tracing ata_eh_link_autopsy event

commit f1601113ddc0339a745e702f4fb1ca37d4875e65 upstream.

When tracing ata link error event, the kernel crashes when the disk is
removed due to NULL pointer access by trace_ata_eh_link_autopsy API.
This occurs as the dev is NULL when the disk disappeared. This patch
fixes this crash by calling trace_ata_eh_link_autopsy only if "dev"
is not NULL.

v2 changes:
 Removed direct passing "link" pointer instead of "dev" in trace API.

Signed-off-by: Rameshwar Prasad Sahu <rsahu@apm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 255c03d ("libata: Add tracepoints")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Rameshwar Prasad Sahu

drivers/ata/libata-eh.c

@@ -2245,8 +2245,8 @@ static void ata_eh_link_autopsy(struct ata_link *link)
 		if (dev->flags & ATA_DFLAG_DUBIOUS_XFER)
 			eflags |= ATA_EFLAG_DUBIOUS_XFER;
 		ehc->i.action |= ata_eh_speed_down(dev, eflags, all_err_mask);
+		trace_ata_eh_link_autopsy(dev, ehc->i.action, all_err_mask);
 	}
-	trace_ata_eh_link_autopsy(dev, ehc->i.action, all_err_mask);
 	DPRINTK("EXIT\n");
 }