"Yan, Zheng" <ukernel@xxxxxxxxx> writes: > On Tue, Mar 19, 2019 at 12:22 AM Luis Henriques <lhenriques@xxxxxxxx> wrote: >> >> "Yan, Zheng" <ukernel@xxxxxxxxx> writes: >> >> > On Mon, Mar 18, 2019 at 6:33 PM Luis Henriques <lhenriques@xxxxxxxx> wrote: >> >> >> >> "Yan, Zheng" <ukernel@xxxxxxxxx> writes: >> >> >> >> > On Fri, Mar 15, 2019 at 7:13 PM Luis Henriques <lhenriques@xxxxxxxx> wrote: >> >> >> >> >> >> I'm occasionally seeing a kmemleak warning in xfstest generic/013: >> >> >> >> >> >> unreferenced object 0xffff8881fccca940 (size 32): >> >> >> comm "kworker/0:1", pid 12, jiffies 4295005883 (age 130.648s) >> >> >> hex dump (first 32 bytes): >> >> >> 01 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 ................ >> >> >> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ >> >> >> backtrace: >> >> >> [<00000000d741a1ea>] build_snap_context+0x5b/0x2a0 >> >> >> [<0000000021a00533>] rebuild_snap_realms+0x27/0x90 >> >> >> [<00000000ac538600>] rebuild_snap_realms+0x42/0x90 >> >> >> [<000000000e955fac>] ceph_update_snap_trace+0x2ee/0x610 >> >> >> [<00000000a9550416>] ceph_handle_snap+0x317/0x5f3 >> >> >> [<00000000fc287b83>] dispatch+0x362/0x176c >> >> >> [<00000000a312c741>] ceph_con_workfn+0x9ce/0x2cf0 >> >> >> [<000000004168e3a9>] process_one_work+0x1d4/0x400 >> >> >> [<000000002188e9e7>] worker_thread+0x2d/0x3c0 >> >> >> [<00000000b593e4b3>] kthread+0x112/0x130 >> >> >> [<00000000a8587dca>] ret_from_fork+0x35/0x40 >> >> >> [<00000000ba1c9c1d>] 0xffffffffffffffff >> >> >> >> >> >> It looks like it is possible that we miss a flush_ack from the MDS when, >> >> >> for example, umounting the filesystem. In that case, we can simply drop >> >> >> the reference to the ceph_snap_context obtained in ceph_queue_cap_snap(). >> >> >> >> >> >> Link: https://tracker.ceph.com/issues/38224 >> >> >> Cc: stable@xxxxxxxxxxxxxxx >> >> >> Signed-off-by: Luis Henriques <lhenriques@xxxxxxxx> >> >> >> --- >> >> >> fs/ceph/caps.c | 7 +++++++ >> >> >> 1 file changed, 7 insertions(+) >> >> >> >> >> >> diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c >> >> >> index 36a8dc699448..208f4dc6f574 100644 >> >> >> --- a/fs/ceph/caps.c >> >> >> +++ b/fs/ceph/caps.c >> >> >> @@ -1054,6 +1054,7 @@ int ceph_is_any_caps(struct inode *inode) >> >> >> static void drop_inode_snap_realm(struct ceph_inode_info *ci) >> >> >> { >> >> >> struct ceph_snap_realm *realm = ci->i_snap_realm; >> >> >> + >> >> >> spin_lock(&realm->inodes_with_caps_lock); >> >> >> list_del_init(&ci->i_snap_realm_item); >> >> >> ci->i_snap_realm_counter++; >> >> >> @@ -1063,6 +1064,12 @@ static void drop_inode_snap_realm(struct ceph_inode_info *ci) >> >> >> spin_unlock(&realm->inodes_with_caps_lock); >> >> >> ceph_put_snap_realm(ceph_sb_to_client(ci->vfs_inode.i_sb)->mdsc, >> >> >> realm); >> >> >> + /* >> >> >> + * ci->i_head_snapc should be NULL, but we may still be waiting for a >> >> >> + * flush_ack from the MDS. In that case, we still hold a ref for the >> >> >> + * ceph_snap_context and we need to drop it. >> >> >> + */ >> >> >> + ceph_put_snap_context(ci->i_head_snapc); >> >> >> } >> >> >> >> >> >> /* >> >> > >> >> > This does not seem right. i_head_snapc is cleared when >> >> > (ci->i_wrbuffer_ref_head == 0 && ci->i_dirty_caps == 0 && >> >> > ci->i_flushing_caps == 0) . Nothing do with dropping ci->i_snap_realm. >> >> > Did you see 'reconnect denied' during the test? If you did, the fix >> >> > should be in iterate_session_caps() >> >> > >> >> >> >> No, I didn't saw any 'reconnect denied' in the test. The test actually >> >> seems to execute fine, except from the memory leak. >> >> >> >> It's very difficult to reproduce this issue, but last time I managed to >> >> get this memory leak to trigger I actually had some debugging code in >> >> drop_inode_snap_realm, something like: >> >> >> >> if (ci->i_head_snapc) >> >> printk("i_head_snapc: 0x%px\n", ci->i_head_snapc); >> > >> > please add code that prints i_wrbuffer_ref_head, i_dirty_caps, >> > i_flushing_caps. and try reproducing it again. >> > >> >> Ok, it took me a few hours, but I managed to reproduce the bug, with >> those extra printks. All those values are set to 0 when the bug >> triggers (and i_head_snapc != NULL). >> > > Thanks, which test triggers this bug? That's generic/013. It usually triggers after a few hours of running it in a loop (I'm using a vstart cluster for that). > > I searched that code, found we may fail to cleanup i_head_snap in two > places. One is in ceph_queue_cap_snap, Another is in > remove_session_caps_cb(). Ah, great! I spent a lot of time looking but I couldn't really find it. My bet was that ceph_queue_cap_snap was doing the ceph_get_snap_context and that the corresponding ceph_put_snap_context would be done in handle_cap_flush_ack. That's why I mentioned the missing flush_ack from MDS. Cheers, -- Luis > >> Cheers, >> -- >> Luis >> >> >> > >> >> >> >> This printk was only executed when the bug triggered (during a >> >> filesystem umount) and the address shown was the same as in the kmemleak >> >> warning. >> >> >> >> After spending some time looking, I assumed this to be a missing call to >> >> handle_cap_flush_ack, which would do the i_head_snapc cleanup. >> >> >> >> Cheers, >> >> -- >> >> Luis >> > >
