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). Cheers, -- Luis
