"Yan, Zheng" <ukernel@xxxxxxxxx> writes: > On Fri, Mar 22, 2019 at 6:04 PM Luis Henriques <lhenriques@xxxxxxxx> wrote: >> >> Luis Henriques <lhenriques@xxxxxxxx> writes: >> >> > "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. >> >> Something that I didn't said explicitly is that I *know* that the >> unbalanced ceph_get_snap_context() is the one in function >> ceph_queue_cap_snap(). I know this for sure because I've managed to >> reproduce the issue several times with an instrumented kernel (with >> tracepoints) that allowed me to keep track of all ceph_snap_context >> operations (create, get, put, delete). >> > > Sorry for the delay. please try Thank you, I'll try the test with your patch applied and see if I still see the issue (obviously, this will take some time as it takes several hours for the bug to trigger). Cheers, -- Luis > > diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c > index 45f061e47721..5bc30e0d252a 100644 > --- a/fs/ceph/mds_client.c > +++ b/fs/ceph/mds_client.c > @@ -1420,6 +1420,15 @@ static int remove_session_caps_cb(struct inode > *inode, struct ceph_cap *cap, > list_add(&ci->i_prealloc_cap_flush->i_list, &to_remove); > ci->i_prealloc_cap_flush = NULL; > } > + > + if (drop && > + ci->i_wrbuffer_ref_head == 0 && > + ci->i_wr_ref == 0 && > + ci->i_dirty_caps == 0 && > + ci->i_flushing_caps == 0) { > + ceph_put_snap_context(ci->i_head_snapc); > + ci->i_head_snapc = NULL; > + } > } > spin_unlock(&ci->i_ceph_lock); > while (!list_empty(&to_remove)) { > diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c > index 89aa37fa0f84..0af4b3d32122 100644 > --- a/fs/ceph/snap.c > +++ b/fs/ceph/snap.c > @@ -572,7 +572,12 @@ void ceph_queue_cap_snap(struct ceph_inode_info *ci) > old_snapc = NULL; > > update_snapc: > - if (ci->i_head_snapc) { > + if (ci->i_wrbuffer_ref_head == 0 && > + ci->i_wr_ref == 0 && > + ci->i_dirty_caps == 0 && > + ci->i_flushing_caps == 0) { > + ci->i_head_snapc = NULL; > + } else { > ci->i_head_snapc = ceph_get_snap_context(new_snapc); > dout(" new snapc is %p\n", new_snapc); > } > > > >> Cheers, >> -- >> Luis >
