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Message-ID: <55F92368.2010004@arm.com> Date: Wed, 16 Sep 2015 09:08:08 +0100 From: "Suzuki K. Poulose" <Suzuki.Poulose@....com> To: Jeff Layton <jlayton@...chiereds.net> CC: Trond Myklebust <trond.myklebust@...marydata.com>, Anna Schumaker <anna.schumaker@...app.com>, "J. Bruce Fields" <bfields@...ldses.org>, "David S. Miller" <davem@...emloft.net>, "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] SUNRPC: Fix a race in xs_reset_transport On 15/09/15 19:52, Jeff Layton wrote: > On Tue, 15 Sep 2015 16:49:23 +0100 > "Suzuki K. Poulose" <suzuki.poulose@....com> wrote: > >> From: "Suzuki K. Poulose" <suzuki.poulose@....com> >> >> Encountered the following BUG() with 4.3-rc1 on a fast model >> for arm64 with NFS root filesystem. >> >> ------------[ cut here ]------------ >> kernel BUG at fs/inode.c:1493! >> >> Internal error: Oops - BUG: 0 [#1] PREEMPT SMP >> Modules linked in: >> CPU: 2 PID: 1 Comm: swapper/0 Not tainted 4.3.0-rc1+ #855 >> Hardware name: FVP Base (DT) >> task: ffffc000760b0000 ti: ffffc00076070000 task.ti: ffffc00076070000 >> PC is at iput+0x144/0x170 >> LR is at sock_release+0xbc/0xdc >> pc : [<ffffc000001b4920>] lr : [<ffffc000004d1974>] pstate: 40000045 >> sp : ffffc00076073790 >> x29: ffffc00076073790 x28: ffffc00076073b40 >> x27: 00000000000003e8 x26: ffffc00076955000 >> x25: 000000000000000c x24: ffffc00076637200 >> x23: ffffc00076073930 x22: ffffc000769b8180 >> x21: ffffc000740500a8 x20: ffffc00074050158 >> x19: ffffc00074050030 x18: 000000009fcef6bf >> x17: 00000000593e3df5 x16: 00000000b597f71d >> x15: 00000000e2f9d3f6 x14: 0ffffffffffffffe >> x13: 0000000000000020 x12: 0101010101010101 >> x11: 00000000000001c9 x10: 0000000000000750 >> x9 : ffffc00076073670 x8 : ffffc000760b07b0 >> x7 : 0000000000000001 x6 : 0000000000000001 >> x5 : 0000000000000000 x4 : 00000000ffffffff >> x3 : 0000000000000000 x2 : ffffffffffffffff >> x1 : ffffc00076070000 x0 : 0000000000000060 >> >> Process swapper/0 (pid: 1, stack limit = 0xffffc00076070020) >> Stack: (0xffffc00076073790 to 0xffffc00076074000) >> >> [ stack contents stripped ] >> >> Call trace: >> [<ffffc000001b4920>] iput+0x144/0x170 >> [<ffffc000004d1970>] sock_release+0xb8/0xdc >> [<ffffc00000578df0>] xs_reset_transport+0x8c/0xac >> [<ffffc00000578e60>] xs_close+0x50/0x6c >> [<ffffc00000578e9c>] xs_destroy+0x20/0x5c >> [<ffffc00000575f70>] xprt_destroy+0x68/0x8c >> [<ffffc0000057777c>] xprt_put+0x24/0x30 >> [<ffffc000005726c4>] rpc_free_client+0x78/0xd8 >> [<ffffc0000057288c>] rpc_release_client+0x94/0xec >> [<ffffc00000572aac>] rpc_shutdown_client+0x58/0x118 >> [<ffffc00000278588>] nfs_mount+0x100/0x234 >> [<ffffc0000026cc88>] nfs_request_mount+0xa8/0x12c >> [<ffffc0000026e564>] nfs_try_mount+0x54/0x2b4 >> [<ffffc0000026f140>] nfs_fs_mount+0x5cc/0xac0 >> [<ffffc0000019f1a0>] mount_fs+0x38/0x158 >> [<ffffc000001b81a8>] vfs_kern_mount+0x48/0x11c >> [<ffffc000001bb390>] do_mount+0x208/0xc04 >> [<ffffc000001bc0b0>] SyS_mount+0x78/0xd0 >> [<ffffc000007f0fa8>] mount_root+0x80/0x148 >> [<ffffc000007f11a8>] prepare_namespace+0x138/0x184 >> [<ffffc000007f0b20>] kernel_init_freeable+0x1cc/0x1f4 >> [<ffffc000005a2914>] kernel_init+0xc/0xd8 >> Code: b5fffc00 17ffffed d4210000 17ffffd7 (d4210000) >> ---[ end trace 02951451f1831f54 ]--- >> >> With rpc_debug enabled here is the log : >> >> RPC: shutting down mount client for your.nfs.server >> RPC: rpc_release_client(ffffc00076637800) >> RPC: destroying UNIX authenticator ffffc000008f48c8 >> RPC: destroying mount client for your.nfs.server >> RPC: destroying transport ffffc00076226000 >> RPC: xs_destroy xprt ffffc00076226000 >> RPC: xs_close xprt ffffc00076226000 >> RPC: xs_tcp_state_change client ffffc00076226000... >> RPC: state 4 conn 1 dead 0 zapped 1 sk_shutdown 3 >> RPC: xs_tcp_state_change client ffffc00076226000... >> RPC: state 5 conn 0 dead 0 zapped 1 sk_shutdown 3 >> RPC: xs_tcp_state_change client ffffc00076226000... >> RPC: state 7 conn 0 dead 0 zapped 1 sk_shutdown 3 >> RPC: disconnected transport ffffc00076226000 >> RPC: xs_tcp_state_change client ffffc00076226000... >> RPC: state 7 conn 0 dead 0 zapped 1 sk_shutdown 3 >> RPC: disconnected transport ffffc00076226000 >> RPC: xs_tcp_data_ready... >> RPC: xs_tcp_state_change client ffffc00076226000... >> RPC: state 7 conn 0 dead 0 zapped 1 sk_shutdown 3 >> RPC: disconnected transport ffffc00076226000 >> RPC: wake_up_first(ffffc00076226170 "xprt_sending") >> >> So it looks like just before we lock the callbacks in xs_reset_transport, >> a few of the callbacks got through and issued the reset before we could >> lock it. And we end up repeating the cleanups, ending up in the above >> BUG() due to multiple sock_release(). >> >> This patch fixes the race by confirming that somebody else hasn't performed >> the reset while we were waiting for the lock. Also, the kernel_shutdown() >> is performed only if the sock is non-NULL to avoid a possible race. >> >> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@....com> >> --- >> net/sunrpc/xprtsock.c | 9 ++++++++- >> 1 file changed, 8 insertions(+), 1 deletion(-) >> >> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c >> index 7be90bc..6f4789d 100644 >> --- a/net/sunrpc/xprtsock.c >> +++ b/net/sunrpc/xprtsock.c >> @@ -822,9 +822,16 @@ static void xs_reset_transport(struct sock_xprt *transport) >> if (atomic_read(&transport->xprt.swapper)) >> sk_clear_memalloc(sk); >> >> - kernel_sock_shutdown(sock, SHUT_RDWR); >> + if (sock) >> + kernel_sock_shutdown(sock, SHUT_RDWR); >> > > Good catch, but...isn't this still racy? What prevents transport->sock > being set to NULL after you assign it to "sock" but before calling > kernel_sock_shutdown? You might end up calling that on a socket that > has already had sock_release called on it. I believe that would be a bad > thing. You are right. I had a try with moving the kernel_sock_shutdown() under the lock, but then it would cause lockups, hence left it there. I should have paid more attention to the kernel_sock_shutdown() which I assumed would be safe :). Thanks for spotting. I will send an updated version. Thanks Suzuki -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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