Do not reserve crashkernel high memory if crashkernel low memory reserving failed

People reported that when allocating crashkernel memory using ",high" and ",low" syntax, there were cases where the reservation of the "high" portion succeeds, but the reservation of the "low" portion fails. Then kexec can load kdump kernel successfully, but the boot of kdump kernel fails as there's no low memory. This is because allocation of low memory for kdump kernel can fail on large systems for reasons. E.g it could be manually specified crashkernel low memory is too large to find in memblock region.

In this patch add return value for reserve_crashkernel_low. Then try to reserve crashkernel low memory after crashkernel high memory has been allocated. If crashkernel low memory reservation failed free crashkernel high memory and return. User can take measures when they found kdump kernel cann't be loaded successfully.

Signed-off-by Baoquan He <[email protected]>

---
v1->v2:
Boris commented that error value EINVAL is negative, should use "return -EINVAL".

v2->v3:
Yinghai pointed out that during memblock_reserve, we could double the memblock reserve array. New memblock reserve could be overlapped with range for crashkernel high. So we have to reserve crashkernel high firstly, then free it if crashkernel low memory allocation failed.

v3->v4:
Dave suggested using "return -ENOMEM" when low memory reservation failed and printing failure message anyway.

v4->v5:
Andrew suggested changing the content of failure message and taking higher severity KERN_ERR.

 arch/x86/kernel/setup.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

arch/x86/kernel/setup.c +11 -9

index fdb7f2a..e510e61 100644
@@ -493,7 +493,7 @@ static void __init memblock_x86_reserve_range_setup_data(void)
 # define CRASH_KERNEL_ADDR_HIGH_MAX	MAXMEM
 #endif
 
-static void __init reserve_crashkernel_low(void)
+static int __init reserve_crashkernel_low(void)
 {
 #ifdef CONFIG_X86_64
 	const unsigned long long alignment = 16<<20;	/* 16M */

@@ -522,17 +522,16 @@ static void __init reserve_crashkernel_low(void)
 	} else {
 		/* passed with crashkernel=0,low ? */
 		if (!low_size)
-			return;
+			return 0;
 	}
 
 	low_base = memblock_find_in_range(low_size, (1ULL<<32),
 					low_size, alignment);
 
 	if (!low_base) {
-		if (!auto_set)
-			pr_info("crashkernel low reservation failed - No suitable area found.\n");
-
-		return;
+		pr_err("Failed to reserve %ldMB of low memory for crashkernel, please try smaller size.\n",
+				(unsigned long)(low_size >> 20));
+		return -ENOMEM;
 	}
 
 	memblock_reserve(low_base, low_size);

@@ -544,6 +543,7 @@ static void __init reserve_crashkernel_low(void)
 	crashk_low_res.end   = low_base + low_size - 1;
 	insert_resource(&iomem_resource, &crashk_low_res);
 #endif
+	return 0;
 }
 
 static void __init reserve_crashkernel(void)

@@ -595,6 +595,11 @@ static void __init reserve_crashkernel(void)
 	}
 	memblock_reserve(crash_base, crash_size);
 
+	if (crash_base >= (1ULL<<32) && reserve_crashkernel_low()) {
+		memblock_free(crash_base, crash_size);
+		return;
+	}
+
 	printk(KERN_INFO "Reserving %ldMB of memory at %ldMB "
 			"for crashkernel (System RAM: %ldMB)\n",
 			(unsigned long)(crash_size >> 20),

@@ -604,9 +609,6 @@ static void __init reserve_crashkernel(void)
 	crashk_res.start = crash_base;
 	crashk_res.end   = crash_base + crash_size - 1;
 	insert_resource(&iomem_resource, &crashk_res);
-
-	if (crash_base >= (1ULL<<32))
-		reserve_crashkernel_low();
 }
 #else
 static void __init reserve_crashkernel(void)

Signature · 1 line

2.4.0

People reported that when allocating crashkernel memory using ",high" and ",low" syntax, there were cases where the reservation of the "high" portion succeeds, but the reservation of the "low" portion fails. Then kexec can load kdump kernel successfully, but the boot of kdump kernel fails as there's no low memory. This is because allocation of low memory for kdump kernel can fail on large systems for reasons. E.g it could be manually specified crashkernel low memory is too large to find in memblock region.

In this patch add return value for reserve_crashkernel_low. Then try to reserve crashkernel low memory after crashkernel high memory has been allocated. If crashkernel low memory reservation failed free crashkernel high memory and return. User can take measures when they found kdump kernel cann't be loaded successfully.

Signed-off-by Baoquan He <[email protected]>

---
v1->v2:
Boris commented that error value EINVAL is negative, should use "return -EINVAL".

v2->v3:
Yinghai pointed out that during memblock_reserve, we could double the memblock reserve array. New memblock reserve could be overlapped with range for crashkernel high. So we have to reserve crashkernel high firstly, then free it if crashkernel low memory allocation failed.

v3->v4:
Dave suggested using "return -ENOMEM" when low memory reservation failed and printing failure message anyway.

v4->v5:
Andrew suggested changing the content of failure message and taking higher severity KERN_ERR.

 arch/x86/kernel/setup.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

Reviewed-by Joerg Roedel <[email protected]>

The patch is also in SLES for some time now and was successfully tested there.