Commit af0ed569 authored by Sage Weil's avatar Sage Weil
Browse files

ceph: fix snap writeback when racing with writes 



There are two problems that come up when we try to queue a capsnap while a
write is in progress:

 - The FILE_WR cap is held, but not yet dirty, so we may queue a capsnap
   with dirty == 0.  That will crash later in __ceph_flush_snaps().  Or
   on the FILE_WR cap if a write is in progress.
 - We may not have i_head_snapc set, which causes problems pretty quickly.
   Look to the snaprealm in this case.

Reviewed-by: default avatarYehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: default avatarSage Weil <sage@newdream.net>
parent 9cfa1098

fs/ceph/snap.c

+20 −3
Original line number Diff line number Diff line
@@ -449,6 +449,15 @@ void ceph_queue_cap_snap(struct ceph_inode_info *ci) 
	spin_lock(&inode->i_lock);

	used = __ceph_caps_used(ci);

	dirty = __ceph_caps_dirty(ci);



	/*

	 * If there is a write in progress, treat that as a dirty Fw,

	 * even though it hasn't completed yet; by the time we finish

	 * up this capsnap it will be.

	 */

	if (used & CEPH_CAP_FILE_WR)

		dirty |= CEPH_CAP_FILE_WR;



	if (__ceph_have_pending_cap_snap(ci)) {

		/* there is no point in queuing multiple "pending" cap_snaps,

		   as no new writes are allowed to start when pending, so any
@@ -456,14 +465,22 @@ void ceph_queue_cap_snap(struct ceph_inode_info *ci) 
		   cap_snap.  lucky us. */

		dout("queue_cap_snap %p already pending\n", inode);

		kfree(capsnap);

	} else if (ci->i_wrbuffer_ref_head || (used & CEPH_CAP_FILE_WR) ||

	} else if (ci->i_wrbuffer_ref_head ||

		   (dirty & (CEPH_CAP_AUTH_EXCL|CEPH_CAP_XATTR_EXCL|

			     CEPH_CAP_FILE_EXCL|CEPH_CAP_FILE_WR))) {

		struct ceph_snap_context *snapc = ci->i_head_snapc;



		dout("queue_cap_snap %p cap_snap %p queuing under %p\n", inode,

		     capsnap, snapc);

		/*

		 * if we are a sync write, we may need to go to the snaprealm

		 * to get the current snapc.

		 */

		if (!snapc)

			snapc = ci->i_snap_realm->cached_context;



		dout("queue_cap_snap %p cap_snap %p queuing under %p %s\n",

		     inode, capsnap, snapc, ceph_cap_string(dirty));

		ihold(inode);

		BUG_ON(dirty == 0);



		atomic_set(&capsnap->nref, 1);

		capsnap->ci = ci;

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