Fix race condition in ext2fs when remounting

On some systems, ext2fs.static would regularly hang at startup, as a
race condition meant it would process paging requests while remounting.
To fix this, libpager has been altered to allow inhibiting and resuming
its worker threads, and ext2fs uses this to inhibit paging while
remounting.

* console/pager.c (pager_requests): New variable.
(user_pager_init): Updated call to pager_start_workers to use new
pager_requests variable.
* daemons/runsystem.sh: Removed artificial delay working around the race
condition.
* ext2fs/ext2fs.c (diskfs_reload_global_state): Call new
inhibit_ext2_pager and resume_ext2_pager functions, and leave sblock as
non-NULL so it will be munmapped.
* ext2fs/ext2fs.h (inhibit_ext2_pager,resume_ext2_pager): New functions.
* ext2fs/pager.c (file_pager_requests): New variable.
(create_disk_pager): Updated call to pager_start_workers to use new
file_pager_requests variable.
(inhibit_ext2_pager,resume_ext2_pager): New functions.
* fatfs/fatfs.h (inhibit_fat_pager,resume_fat_pager): New functions.
* fatfs/pager.c (file_pager_requests): New variable.
(create_fat_pager): Updated call to pager_start_workers to use new
file_pager_requests variable.
(inhibit_fat_pager,resume_fat_pager): New functions.
* libdiskfs/disk-pager.c (diskfs_disk_pager_requests): New variable.
(diskfs_start_disk_pager): Updated call to pager_start_workers to use
new diskfs_disk_pager_requests variable.
* libdiskfs/diskfs-pager.h (diskfs_disk_pager_requests): New variable.
* libpager/demuxer.c (struct pager_requests): Renamed struct requests to
struct pager_requests. Replaced queue with queue_in and queue_out
pointers. Added inhibit_wakeup field.
(pager_demuxer): Updated to use new queue_in/queue_out pointers. Only
wake up workers if not inhibited.
(worker_func): Updated to use new queue_in/queue_out pointers. Final
worker thread to sleep notifies the inhibit_wakeup condition variable.
(pager_start_workers): Added out parameter for the requests instance.
Allocate heap space shared by both queues. Initialise new inhibit_wakeup
condition.
(pager_inhibit_workers,pager_resume_workers): New functions.
* libpager/pager.h (struct pager_requests): Public forward definition.
(pager_start_workers): Added out parameter for the requests instance.
(pager_inhibit_workers,pager_resume_workers): New functions.
* libpager/queue.h (queue_empty): New function.
* storeio/pager.c (pager_requests): New variable.
(init_dev_paging): Updated call to pager_start_workers to use new
pager_requests variable.

2 files changed, 3 insertions, 1 deletions

diff --git a/libdiskfs/disk-pager.c b/libdiskfs/disk-pager.c
index 008aa2dc..434ceed9 100644
--- a/libdiskfs/disk-pager.c
+++ b/libdiskfs/disk-pager.c
@@ -24,6 +24,7 @@
 __thread struct disk_image_user *diskfs_exception_diu;
 
 struct pager *diskfs_disk_pager;
+struct pager_requests *diskfs_disk_pager_requests;
 
 static void fault_handler (int sig, long int sigcode, struct sigcontext *scp);
 static struct hurd_signal_preemptor preemptor =
@@ -43,7 +44,7 @@ diskfs_start_disk_pager (struct user_pager_info *upi,
   mach_port_t disk_pager_port;
 
   /* Start libpagers worker threads.  */
-  err = pager_start_workers (pager_bucket);
+  err = pager_start_workers (pager_bucket, &diskfs_disk_pager_requests);
   if (err)
     error (2, err, "creating pager worker threads failed");
 
diff --git a/libdiskfs/diskfs-pager.h b/libdiskfs/diskfs-pager.h
index a253069b..550ca644 100644
--- a/libdiskfs/diskfs-pager.h
+++ b/libdiskfs/diskfs-pager.h
@@ -40,6 +40,7 @@ extern void diskfs_start_disk_pager (struct user_pager_info *info,
 				     size_t size, void **image);
 
 extern struct pager *diskfs_disk_pager;
+extern struct pager_requests *diskfs_disk_pager_requests;
 
 struct disk_image_user
   {