xfs: create shadow transaction reservations for computing minimum log size

Every time someone changes the transaction reservation sizes, they
introduce potential compatibility problems if the changes affect the
minimum log size that we validate at mount time.  If the minimum log
size gets larger (which should be avoided because doing so presents a
serious risk of log livelock), filesystems created with old mkfs will
not mount on a newer kernel; if the minimum size shrinks, filesystems
created with newer mkfs will not mount on older kernels.

Therefore, enable the creation of a shadow log reservation structure
where we can "undo" the effects of tweaks when computing minimum log
sizes.  These shadow reservations should never be used in practice, but
they insulate us from perturbations in minimum log size.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>

4 files changed, 37 insertions, 6 deletions

diff --git a/fs/xfs/libxfs/xfs_log_rlimit.c b/fs/xfs/libxfs/xfs_log_rlimit.c
index 67798ff5e14e..2bafc69cac15 100644
--- a/fs/xfs/libxfs/xfs_log_rlimit.c
+++ b/fs/xfs/libxfs/xfs_log_rlimit.c
@@ -14,6 +14,7 @@
 #include "xfs_trans_space.h"
 #include "xfs_da_btree.h"
 #include "xfs_bmap_btree.h"
+#include "xfs_trace.h"
 
 /*
  * Calculate the maximum length in bytes that would be required for a local
@@ -47,18 +48,25 @@ xfs_log_get_max_trans_res(
 	struct xfs_trans_res	*max_resp)
 {
 	struct xfs_trans_res	*resp;
+	struct xfs_trans_res	*start_resp;
 	struct xfs_trans_res	*end_resp;
+	struct xfs_trans_resv	*resv;
 	int			log_space = 0;
 	int			attr_space;
 
 	attr_space = xfs_log_calc_max_attrsetm_res(mp);
 
-	resp = (struct xfs_trans_res *)M_RES(mp);
-	end_resp = (struct xfs_trans_res *)(M_RES(mp) + 1);
-	for (; resp < end_resp; resp++) {
+	resv = kmem_zalloc(sizeof(struct xfs_trans_resv), 0);
+	xfs_trans_resv_calc_logsize(mp, resv);
+
+	start_resp = (struct xfs_trans_res *)resv;
+	end_resp = (struct xfs_trans_res *)(resv + 1);
+	for (resp = start_resp; resp < end_resp; resp++) {
 		int		tmp = resp->tr_logcount > 1 ?
 				      resp->tr_logres * resp->tr_logcount :
 				      resp->tr_logres;
+
+		trace_xfs_trans_resv_calc_logsize(mp, resp - start_resp, resp);
 		if (log_space < tmp) {
 			log_space = tmp;
 			*max_resp = *resp;		/* struct copy */
@@ -66,9 +74,10 @@ xfs_log_get_max_trans_res(
 	}
 
 	if (attr_space > log_space) {
-		*max_resp = M_RES(mp)->tr_attrsetm;	/* struct copy */
+		*max_resp = resv->tr_attrsetm;	/* struct copy */
 		max_resp->tr_logres = attr_space;
 	}
+	kmem_free(resv);
 }
 
 /*
diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c
index 5e300daa2559..852c16ce8c43 100644
--- a/fs/xfs/libxfs/xfs_trans_resv.c
+++ b/fs/xfs/libxfs/xfs_trans_resv.c
@@ -917,3 +917,15 @@ xfs_trans_resv_calc(
 	resp->tr_growrtzero.tr_logres = xfs_calc_growrtzero_reservation(mp);
 	resp->tr_growrtfree.tr_logres = xfs_calc_growrtfree_reservation(mp);
 }
+
+/*
+ * Compute an alternate set of log reservation sizes for use exclusively with
+ * minimum log size calculations.
+ */
+void
+xfs_trans_resv_calc_logsize(
+	struct xfs_mount	*mp,
+	struct xfs_trans_resv	*resp)
+{
+	xfs_trans_resv_calc(mp, resp);
+}
diff --git a/fs/xfs/libxfs/xfs_trans_resv.h b/fs/xfs/libxfs/xfs_trans_resv.h
index fc4e9b369a3a..9fa4863f72a4 100644
--- a/fs/xfs/libxfs/xfs_trans_resv.h
+++ b/fs/xfs/libxfs/xfs_trans_resv.h
@@ -89,6 +89,8 @@ struct xfs_trans_resv {
 #define	XFS_ATTRSET_LOG_COUNT		3
 #define	XFS_ATTRRM_LOG_COUNT		3
 
+void xfs_trans_resv_calc_logsize(struct xfs_mount *mp,
+		struct xfs_trans_resv *resp);
 void xfs_trans_resv_calc(struct xfs_mount *mp, struct xfs_trans_resv *resp);
 uint xfs_allocfree_log_count(struct xfs_mount *mp, uint num_ops);
 
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 1033a95fbf8e..e0c788d0f9ed 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -3513,7 +3513,7 @@ DEFINE_GETFSMAP_EVENT(xfs_getfsmap_low_key);
 DEFINE_GETFSMAP_EVENT(xfs_getfsmap_high_key);
 DEFINE_GETFSMAP_EVENT(xfs_getfsmap_mapping);
 
-TRACE_EVENT(xfs_trans_resv_calc,
+DECLARE_EVENT_CLASS(xfs_trans_resv_class,
 	TP_PROTO(struct xfs_mount *mp, unsigned int type,
 		 struct xfs_trans_res *res),
 	TP_ARGS(mp, type, res),
@@ -3537,7 +3537,15 @@ TRACE_EVENT(xfs_trans_resv_calc,
 		  __entry->logres,
 		  __entry->logcount,
 		  __entry->logflags)
-);
+)
+
+#define DEFINE_TRANS_RESV_EVENT(name) \
+DEFINE_EVENT(xfs_trans_resv_class, name, \
+	TP_PROTO(struct xfs_mount *mp, unsigned int type, \
+		 struct xfs_trans_res *res), \
+	TP_ARGS(mp, type, res))
+DEFINE_TRANS_RESV_EVENT(xfs_trans_resv_calc);
+DEFINE_TRANS_RESV_EVENT(xfs_trans_resv_calc_logsize);
 
 DECLARE_EVENT_CLASS(xfs_trans_class,
 	TP_PROTO(struct xfs_trans *tp, unsigned long caller_ip),