Hi, I've just hit a deadlock in NFS that seems very strange. The kernel is 3.14-rc8 which some local changes which shouldn't affect the deadlocking code. Shortly after umounting the NFS filesystem with "umount -f" (though I don't think the -f is important), I ran "sync". The sync is now stuck in [<ffffffff81197fc1>] sync_inodes_sb+0xa1/0x1c0 [<ffffffff8119cd99>] sync_inodes_one_sb+0x19/0x20 [<ffffffff81173372>] iterate_supers+0xb2/0x110 [<ffffffff8119cfd0>] sys_sync+0x30/0x90 [<ffffffff81aa4622>] system_call_fastpath+0x16/0x1b [<ffffffffffffffff>] 0xffffffffffffffff while kworker/u16:1 is stuck: [<ffffffff815420b3>] call_rwsem_down_write_failed+0x13/0x20 [<ffffffff81172889>] deactivate_super+0x39/0x60 [<ffffffff812d56f1>] nfs_sb_deactive+0x21/0x30 [<ffffffff812d2ef9>] __put_nfs_open_context+0xc9/0x100 [<ffffffff812d2f3b>] put_nfs_open_context+0xb/0x10 [<ffffffff812ddd14>] nfs_commitdata_release+0x14/0x30 [<ffffffff812ddd4a>] nfs_commit_release+0x1a/0x20 [<ffffffff81a45a05>] rpc_free_task+0x25/0x70 [<ffffffff81a45fd8>] rpc_do_put_task+0x78/0x80 [<ffffffff81a45feb>] rpc_put_task+0xb/0x10 [<ffffffff812de3fe>] nfs_initiate_commit+0xce/0x110 [<ffffffff812df112>] nfs_commit_list+0x62/0x90 [<ffffffff812dfd26>] nfs_commit_inode+0xa6/0x170 [<ffffffff812dfe4d>] nfs_write_inode+0x5d/0xa0 [<ffffffff81300d69>] nfs4_write_inode+0x9/0x10 [<ffffffff811978ec>] __writeback_single_inode+0x10c/0x2c0 [<ffffffff811987ea>] writeback_sb_inodes+0x2ca/0x450 [<ffffffff81198b2c>] wb_writeback+0xec/0x320 [<ffffffff81199365>] bdi_writeback_workfn+0x115/0x4c0 [<ffffffff810a595b>] process_one_work+0x16b/0x430 [<ffffffff810a6619>] worker_thread+0x119/0x3a0 [<ffffffff810ac2bd>] kthread+0xcd/0xf0 [<ffffffff81aa457c>] ret_from_fork+0x7c/0xb0 [<ffffffffffffffff>] 0xffffffffffffffff So sync is holding sb->s_umount, queued some bdi work on the filesystem and is waiting for it to complete. Mean while, that work has (I think) submitted a 'commit' (via ->write_inode) and that commit wants to deactivate_super and so needs to get ->s_umount. I suspect this could happen even more easily with a lazy unmount. It seems that this commit request is that last thing that is keeping ->s_active elevated and it deadlocks trying to drop the last s_active. I have no idea how to fix it.... help? NeilBrown
Attachment:
signature.asc
Description: PGP signature
