Giant pushdown for read/write/pread/pwrite syscalls.

kern/kern_descrip.c:
Aquire Giant in fdrop_locked when file refcount hits zero, this removes
the requirement for the caller to own Giant for the most part.

kern/kern_ktrace.c:
Aquire Giant in ktrgenio, simplifies locking in upper read/write syscalls.

kern/vfs_bio.c:
Aquire Giant in bwillwrite if needed.

kern/sys_generic.c
Giant pushdown, remove Giant for:
   read, pread, write and pwrite.
readv and writev aren't done yet because of the possible malloc calls
for iov to uio processing.

kern/sys_socket.c
Grab giant in the socket fo_read/write functions.

kern/vfs_vnops.c
Grab giant in the vnode fo_read/write functions.

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index 70d3a92..bf4970d 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -1079,6 +1079,7 @@ bwillwrite(void)
 	if (numdirtybuffers >= hidirtybuffers) {
 		int s;
 
+		mtx_lock(&Giant);
 		s = splbio();
 		while (numdirtybuffers >= hidirtybuffers) {
 			bd_wakeup(1);
@@ -1086,6 +1087,7 @@ bwillwrite(void)
 			tsleep(&needsbuffer, (PRIBIO + 4), "flswai", 0);
 		}
 		splx(s);
+		mtx_unlock(&Giant);
 	}
 }