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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: Yehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: Sage Weil <sage@newdream.net>
This commit is contained in:
Sage Weil 2011-07-26 11:26:31 -07:00
parent 9cfa1098dc
commit af0ed569d7
1 changed files with 20 additions and 3 deletions
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23
fs/ceph/snap.c
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@ -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;