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authorNeilBrown <neilb@suse.de>2014-04-09 14:33:51 +1000
committerNeilBrown <neilb@suse.de>2014-04-09 14:42:34 +1000
commite2f23b606b94f28a8febd5aa715df697d80b018e (patch)
treed9f21bd649683bedbdadb301b1533c09e13591ba /drivers
parentda1aab3dca9aa88ae34ca392470b8943159e25fe (diff)
downloadlinux-e2f23b606b94f28a8febd5aa715df697d80b018e.tar.bz2
md: avoid oops on unload if some process is in poll or select.
If md-mod is unloaded while some process is in poll() or select(), then that process maintains a pointer to md_event_waiters, and when the try to unlink from that list, they will oops. The procfs infrastructure ensures that ->poll won't be called after remove_proc_entry, but doesn't provide a wait_queue_head for us to use, and the waitqueue code doesn't provide a way to remove all listeners from a waitqueue. So we need to: 1/ make sure no further references to md_event_waiters are taken (by setting md_unloading) 2/ wake up all processes currently waiting, and 3/ wait until all those processes have disconnected from our wait_queue_head. Reported-by: "majianpeng" <majianpeng@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/md/md.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 3fa2fc0a5dd2..8fda38d23e38 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7165,11 +7165,14 @@ static int md_seq_open(struct inode *inode, struct file *file)
return error;
}
+static int md_unloading;
static unsigned int mdstat_poll(struct file *filp, poll_table *wait)
{
struct seq_file *seq = filp->private_data;
int mask;
+ if (md_unloading)
+ return POLLIN|POLLRDNORM|POLLERR|POLLPRI;;
poll_wait(filp, &md_event_waiters, wait);
/* always allow read */
@@ -8655,6 +8658,7 @@ static __exit void md_exit(void)
{
struct mddev *mddev;
struct list_head *tmp;
+ int delay = 1;
blk_unregister_region(MKDEV(MD_MAJOR,0), 1U << MINORBITS);
blk_unregister_region(MKDEV(mdp_major,0), 1U << MINORBITS);
@@ -8663,7 +8667,19 @@ static __exit void md_exit(void)
unregister_blkdev(mdp_major, "mdp");
unregister_reboot_notifier(&md_notifier);
unregister_sysctl_table(raid_table_header);
+
+ /* We cannot unload the modules while some process is
+ * waiting for us in select() or poll() - wake them up
+ */
+ md_unloading = 1;
+ while (waitqueue_active(&md_event_waiters)) {
+ /* not safe to leave yet */
+ wake_up(&md_event_waiters);
+ msleep(delay);
+ delay += delay;
+ }
remove_proc_entry("mdstat", NULL);
+
for_each_mddev(mddev, tmp) {
export_array(mddev);
mddev->hold_active = 0;