----- Original Message ----- > From: "Pranith Kumar Karampuri" <pkara...@redhat.com> > To: "Krutika Dhananjay" <kdhan...@redhat.com>, "Anand Avati" > <aav...@redhat.com> > Cc: gluster-devel@gluster.org > Sent: Wednesday, June 4, 2014 12:23:59 PM > Subject: Re: [Gluster-devel] Regarding doing away with refkeeper in locks > xlator
> On 06/04/2014 12:02 PM, Pranith Kumar Karampuri wrote: > > On 06/04/2014 11:37 AM, Krutika Dhananjay wrote: > > > > Hi, > > > > > > Recently there was a crash in locks translator (BZ 1103347, BZ 1097102) > > > with > > > the following backtrace: > > > > > > (gdb) bt > > > > > > #0 uuid_unpack (in=0x8 <Address 0x8 out of bounds>, uu=0x7fffea6c6a60) at > > > ../../contrib/uuid/unpack.c:44 > > > > > > #1 0x00007feeba9e19d6 in uuid_unparse_x (uu=<value optimized out>, > > > out=0x2350fc0 "081bbc7a-7551-44ac-85c7-aad5e2633db9", > > > > > > fmt=0x7feebaa08e00 "%08x-%04x-%04x-%02x%02x-%02x%02x%02x%02x%02x%02x") at > > > ../../contrib/uuid/unparse.c:55 > > > > > > #2 0x00007feeba9be837 in uuid_utoa (uuid=0x8 <Address 0x8 out of bounds>) > > > at > > > common-utils.c:2138 > > > > > > #3 0x00007feeb06e8a58 in pl_inodelk_log_cleanup (this=0x230d910, > > > ctx=0x7fee700f0c60) at inodelk.c:396 > > > > > > #4 pl_inodelk_client_cleanup (this=0x230d910, ctx=0x7fee700f0c60) at > > > inodelk.c:428 > > > > > > #5 0x00007feeb06ddf3a in pl_client_disconnect_cbk (this=0x230d910, > > > client=<value optimized out>) at posix.c:2550 > > > > > > #6 0x00007feeba9fa2dd in gf_client_disconnect (client=0x27724a0) at > > > client_t.c:368 > > > > > > #7 0x00007feeab77ed48 in server_connection_cleanup (this=0x2316390, > > > client=0x27724a0, flags=<value optimized out>) at server-helpers.c:354 > > > > > > #8 0x00007feeab77ae2c in server_rpc_notify (rpc=<value optimized out>, > > > xl=0x2316390, event=<value optimized out>, data=0x2bf51c0) at > > > server.c:527 > > > > > > #9 0x00007feeba775155 in rpcsvc_handle_disconnect (svc=0x2325980, > > > trans=0x2bf51c0) at rpcsvc.c:720 > > > > > > #10 0x00007feeba776c30 in rpcsvc_notify (trans=0x2bf51c0, mydata=<value > > > optimized out>, event=<value optimized out>, data=0x2bf51c0) at > > > rpcsvc.c:758 > > > > > > #11 0x00007feeba778638 in rpc_transport_notify (this=<value optimized > > > out>, > > > event=<value optimized out>, data=<value optimized out>) at > > > rpc-transport.c:512 > > > > > > #12 0x00007feeb115e971 in socket_event_poll_err (fd=<value optimized > > > out>, > > > idx=<value optimized out>, data=0x2bf51c0, poll_in=<value optimized out>, > > > poll_out=0, > > > > > > poll_err=0) at socket.c:1071 > > > > > > #13 socket_event_handler (fd=<value optimized out>, idx=<value optimized > > > out>, data=0x2bf51c0, poll_in=<value optimized out>, poll_out=0, > > > poll_err=0) > > > at socket.c:2240 > > > > > > #14 0x00007feeba9fc6a7 in event_dispatch_epoll_handler > > > (event_pool=0x22e2d00) > > > at event-epoll.c:384 > > > > > > #15 event_dispatch_epoll (event_pool=0x22e2d00) at event-epoll.c:445 > > > > > > #16 0x0000000000407e93 in main (argc=19, argv=0x7fffea6c7f88) at > > > glusterfsd.c:2023 > > > > > > (gdb) f 4 > > > > > > #4 pl_inodelk_client_cleanup (this=0x230d910, ctx=0x7fee700f0c60) at > > > inodelk.c:428 > > > > > > 428 pl_inodelk_log_cleanup (l); > > > > > > (gdb) p l->pl_inode->refkeeper > > > > > > $1 = (inode_t *) 0x0 > > > > > > (gdb) > > > > > > pl_inode->refkeeper was found to be NULL even when there were some > > > blocked > > > inodelks in a certain domain of the inode, > > > > > > which when dereferenced by the epoll thread in the cleanup codepath led > > > to > > > a > > > crash. > > > > > > On inspecting the code (for want of a consistent reproducer), three > > > things > > > were found: > > > > > > 1. The function where the crash happens (pl_inodelk_log_cleanup()), makes > > > an > > > attempt to resolve the inode to path as can be seen below. But the way > > > inode_path() itself > > > > > > works is to first construct the path based on the given inode's ancestry > > > and > > > place it in the buffer provided. And if all else fails, the gfid of the > > > inode is placed in a certain format ("<gfid:%s>"). > > > > > > This eliminates the need for statements from line 4 through 7 below, > > > thereby > > > "preventing" dereferencing of pl_inode->refkeeper. > > > > > > Now, although this change prevents the crash altogether, it still does > > > not > > > fix the race that led to pl_inode->refkeeper becoming NULL, and comes at > > > the > > > cost of > > > > > > printing "(null)" in the log message on line 9 every time > > > pl_inode->refkeeper > > > is found to be NULL, rendering the logged messages somewhat useless. > > > > > > <code> > > > > > > 0 pl_inode = lock->pl_inode; > > > > > > 1 > > > > > > 2 inode_path (pl_inode->refkeeper, NULL, &path); > > > > > > 3 > > > > > > 4 if (path) > > > > > > 5 file = path; > > > > > > 6 else > > > > > > 7 file = uuid_utoa (pl_inode->refkeeper->gfid); > > > > > > 8 > > > > > > 9 gf_log (THIS->name, GF_LOG_WARNING, > > > > > > 10 "releasing lock on %s held by " > > > > > > 11 "{client=%p, pid=%"PRId64" lk-owner=%s}", > > > > > > 12 file, lock->client, (uint64_t) lock->client_pid, > > > > > > 13 lkowner_utoa (&lock->owner)); > > > > > > <\code> > > > > > I think this logging code is from the days when gfid handle concept was not > > there. So it wasn't returning <gfid:gfid-str> in cases the path is not > > present in the dentries. I believe the else block can be deleted safely > > now. > > > Pranith > Posted patch http://review.gluster.org/#/c/7981/1 for review, to fix problem #1 above. -Krutika > > > 2. There is at least one codepath found that can lead to this crash: > > > > > > Imagine an inode on which an inodelk operation is attempted by a client > > > and > > > is successfully granted too. > > > > > > Now, between the time the lock was granted and pl_update_refkeeper() was > > > called by this thread, the client could send a DISCONNECT event, > > > > > > causing cleanup codepath to be executed, where the epoll thread crashes > > > on > > > dereferencing pl_inode->refkeeper which is STILL NULL at this point. > > > > > > Besides, there are still places in locks xlator where the refkeeper is > > > NOT > > > updated whenever the lists are modified - for instance in the cleanup > > > codepath from a DISCONNECT. > > > > > > 3. Also, pl_update_refkeeper() seems to be not taking into account > > > blocked > > > locks on the inode in the __pl_inode_is_empty() check, when it should, as > > > there could still be cases > > > > > > where the granted list could be empty but not the blocked list at the > > > time > > > of > > > udpating the refkeeper, in which case pl_inode must still take ref on the > > > inode. > > > > > Avati, > > > There is one more issue, where pl_inode_forget is cleaning up > > blocked/granted > > locks which is not handling the new 'client_list'. But if we fix inode > > ref/unref like Kritika proposed, pl_forget should never come when there is > > a > > granted/blocked lock. So may be we should delete that as well. Please feel > > free to comment. > > It is pl_forget not pl_inode_forget. typo :-(. > Pranith > > Pranith > > > > Proposed solution to 2/3: > > > > > > 1. Do away with refkeeper in pl_inode_t altogether. > > > > > > 2. Let every lock object (inodelk/entryllk/posix_lock) have an inode_t * > > > member to act as a placeholder for the associated inode object on which > > > it > > > is locking. > > > > > > 3. Let each lock object hold a ref on the inode at the time of its > > > creation > > > and unref the inode during its destruction. > > > > > > Please let me know what you think of the above. > > > > > > -Krutika > > > > > > _______________________________________________ > > > > > > Gluster-devel mailing list Gluster-devel@gluster.org > > > http://supercolony.gluster.org/mailman/listinfo/gluster-devel > > > > > _______________________________________________ > > > Gluster-devel mailing list Gluster-devel@gluster.org > > http://supercolony.gluster.org/mailman/listinfo/gluster-devel >
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