On Fri, 1 May 2015, Benjamin Coddington wrote: > On Wed, 4 Mar 2015, Shawn Bohrer wrote: > > > Hello, > > > > We're using the Linux cgroup Freezer on some machines that use NFS and > > have run into what appears to be a bug where frozen tasks are blocking > > running tasks and preventing them from completing. On one of our > > machines which happens to be running an older 3.10.46 kernel we have > > frozen some of the tasks on the system using the cgroup Freezer. We > > also have a separate set of tasks which are NOT frozen which are stuck > > trying to open some files on NFS. > > > > Looking at the frozen tasks there are several that have the following > > stack: > > > > [<ffffffff814fd055>] rpc_wait_bit_killable+0x35/0x80 > > [<ffffffff814fd01d>] __rpc_wait_for_completion_task+0x2d/0x30 > > [<ffffffff811dce5d>] nfs4_run_open_task+0x11d/0x170 > > [<ffffffff811de7a3>] _nfs4_open_and_get_state+0x53/0x260 > > [<ffffffff811e12d1>] nfs4_do_open+0x121/0x400 > > [<ffffffff811e15e1>] nfs4_atomic_open+0x31/0x50 > > [<ffffffff811f02dc>] nfs4_file_open+0xac/0x180 > > [<ffffffff811479be>] do_dentry_open.isra.19+0x1ee/0x280 > > [<ffffffff81147b3e>] finish_open+0x1e/0x30 > > [<ffffffff811578d2>] do_last.isra.64+0x2c2/0xc40 > > [<ffffffff81158519>] path_openat.isra.65+0x2c9/0x490 > > [<ffffffff81158c38>] do_filp_open+0x38/0x80 > > [<ffffffff81148cd4>] do_sys_open+0xe4/0x1c0 > > [<ffffffff81148dce>] SyS_open+0x1e/0x20 > > [<ffffffff8153e719>] system_call_fastpath+0x16/0x1b > > [<ffffffffffffffff>] 0xffffffffffffffff > > > > Here it looks like we are waiting in a wait queue inside > > rpc_wait_bit_killable() for RPC_TASK_ACTIVE. > > > > And there is a single task with a stack that looks like the following: > > > > [<ffffffff8107dc05>] __refrigerator+0x55/0x150 > > [<ffffffff814fd086>] rpc_wait_bit_killable+0x66/0x80 > > [<ffffffff814fd01d>] __rpc_wait_for_completion_task+0x2d/0x30 > > [<ffffffff811dce5d>] nfs4_run_open_task+0x11d/0x170 > > [<ffffffff811de7a3>] _nfs4_open_and_get_state+0x53/0x260 > > [<ffffffff811e12d1>] nfs4_do_open+0x121/0x400 > > [<ffffffff811e15e1>] nfs4_atomic_open+0x31/0x50 > > [<ffffffff811f02dc>] nfs4_file_open+0xac/0x180 > > [<ffffffff811479be>] do_dentry_open.isra.19+0x1ee/0x280 > > [<ffffffff81147b3e>] finish_open+0x1e/0x30 > > [<ffffffff811578d2>] do_last.isra.64+0x2c2/0xc40 > > [<ffffffff81158519>] path_openat.isra.65+0x2c9/0x490 > > [<ffffffff81158c38>] do_filp_open+0x38/0x80 > > [<ffffffff81148cd4>] do_sys_open+0xe4/0x1c0 > > [<ffffffff81148dce>] SyS_open+0x1e/0x20 > > [<ffffffff8153e719>] system_call_fastpath+0x16/0x1b > > [<ffffffffffffffff>] 0xffffffffffffffff > > > > This looks similar but the different offset into > > rpc_wait_bit_killable() shows that we have returned from the > > schedule() call in freezable_schedule() and are now blocked in > > __refrigerator() inside freezer_count() > > > > Similarly if you look at the tasks that are NOT frozen but are stuck > > opening a NFS file, they also have the following stack showing they are > > waiting in the wait queue for RPC_TASK_ACTIVE. > > > > [<ffffffff814fd055>] rpc_wait_bit_killable+0x35/0x80 > > [<ffffffff814fd01d>] __rpc_wait_for_completion_task+0x2d/0x30 > > [<ffffffff811dce5d>] nfs4_run_open_task+0x11d/0x170 > > [<ffffffff811de7a3>] _nfs4_open_and_get_state+0x53/0x260 > > [<ffffffff811e12d1>] nfs4_do_open+0x121/0x400 > > [<ffffffff811e15e1>] nfs4_atomic_open+0x31/0x50 > > [<ffffffff811f02dc>] nfs4_file_open+0xac/0x180 > > [<ffffffff811479be>] do_dentry_open.isra.19+0x1ee/0x280 > > [<ffffffff81147b3e>] finish_open+0x1e/0x30 > > [<ffffffff811578d2>] do_last.isra.64+0x2c2/0xc40 > > [<ffffffff81158519>] path_openat.isra.65+0x2c9/0x490 > > [<ffffffff81158c38>] do_filp_open+0x38/0x80 > > [<ffffffff81148cd4>] do_sys_open+0xe4/0x1c0 > > [<ffffffff81148dce>] SyS_open+0x1e/0x20 > > [<ffffffff8153e719>] system_call_fastpath+0x16/0x1b > > [<ffffffffffffffff>] 0xffffffffffffffff > > > > We have hit this a couple of times now and know that if we THAW all of > > the frozen tasks that running tasks will unwedge and finish. > > > > Additionally we have also tried thawing the single task that is frozen > > in __refrigerator() inside rpc_wait_bit_killable(). This usually > > results in different frozen task entering the __refrigerator() state > > inside rpc_wait_bit_killable(). It looks like each one of those tasks > > must wake up another letting it progress. Again if you thaw enough of > > the frozen tasks eventually everything unwedges and everything > > completes. > > > > I've looked through the 3.10 stable patches since 3.10.46 and don't > > see anything that looks like it addresses this. Does anyone have any > > idea what might be going on here, and what the fix might be? > > > > Thanks, > > Shawn > > Hi Shawn, just started looking at this myself, and as Frank Sorensen points > out in https://bugzilla.redhat.com/show_bug.cgi?id=1209143 the problem is > that a task takes the xprt lock and then ends up in the refrigerator > effectively blocking other tasks from proceeding. > > Jeff, any suggestions on how to proceed here? Sorry for the noise, and self-reply.. Looks like there's additional context here: http://marc.info/?t=136761512100007&r=1&w=2 Due to a number of locking problems the answer to this problem is likely to be "don't do that" for now. Ben -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
