[PATCH 5.10 053/126] net: 9p: advance iov on empty read

Greg Kroah-Hartman
2021-04-05T09:10:34Z

From: Jisheng Zhang <Jisheng.Zhang@synaptics.com>

[ Upstream commit d65614a01d24704b016635abf5cc028a54e45a62 ]

I met below warning when cating a small size(about 80bytes) txt file
on 9pfs(msize=2097152 is passed to 9p mount option), the reason is we
miss iov_iter_advance() if the read count is 0 for zerocopy case, so
we didn't truncate the pipe, then iov_iter_pipe() thinks the pipe is
full. Fix it by removing the exception for 0 to ensure to call
iov_iter_advance() even on empty read for zerocopy case.

[ 8.279568] WARNING: CPU: 0 PID: 39 at lib/iov_iter.c:1203 iov_iter_pipe+0x31/0x40
[ 8.280028] Modules linked in:
[ 8.280561] CPU: 0 PID: 39 Comm: cat Not tainted 5.11.0+ #6
[ 8.281260] RIP: 0010:iov_iter_pipe+0x31/0x40
[ 8.281974] Code: 2b 42 54 39 42 5c 76 22 c7 07 20 00 00 00 48 89 57 18 8b 42 50 48 c7 47 08 b
[ 8.283169] RSP: 0018:ffff888000cbbd80 EFLAGS: 00000246
[ 8.283512] RAX: 0000000000000010 RBX: ffff888000117d00 RCX: 0000000000000000
[ 8.283876] RDX: ffff88800031d600 RSI: 0000000000000000 RDI: ffff888000cbbd90
[ 8.284244] RBP: ffff888000cbbe38 R08: 0000000000000000 R09: ffff8880008d2058
[ 8.284605] R10: 0000000000000002 R11: ffff888000375510 R12: 0000000000000050
[ 8.284964] R13: ffff888000cbbe80 R14: 0000000000000050 R15: ffff88800031d600
[ 8.285439] FS: 00007f24fd8af600(0000) GS:ffff88803ec00000(0000) knlGS:0000000000000000
[ 8.285844] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 8.286150] CR2: 00007f24fd7d7b90 CR3: 0000000000c97000 CR4: 00000000000406b0
[ 8.286710] Call Trace:
[ 8.288279] generic_file_splice_read+0x31/0x1a0
[ 8.289273] ? do_splice_to+0x2f/0x90
[ 8.289511] splice_direct_to_actor+0xcc/0x220
[ 8.289788] ? pipe_to_sendpage+0xa0/0xa0
[ 8.290052] do_splice_direct+0x8b/0xd0
[ 8.290314] do_sendfile+0x1ad/0x470
[ 8.290576] do_syscall_64+0x2d/0x40
[ 8.290818] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 8.291409] RIP: 0033:0x7f24fd7dca0a
[ 8.292511] Code: c3 0f 1f 80 00 00 00 00 4c 89 d2 4c 89 c6 e9 bd fd ff ff 0f 1f 44 00 00 31 8
[ 8.293360] RSP: 002b:00007ffc20932818 EFLAGS: 00000206 ORIG_RAX: 0000000000000028
[ 8.293800] RAX: ffffffffffffffda RBX: 0000000001000000 RCX: 00007f24fd7dca0a
[ 8.294153] RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000001
[ 8.294504] RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
[ 8.294867] R10: 0000000001000000 R11: 0000000000000206 R12: 0000000000000003
[ 8.295217] R13: 0000000000000001 R14: 0000000000000001 R15: 0000000000000000
[ 8.295782] ---[ end trace 63317af81b3ca24b ]---

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/9p/client.c | 4 ----
1 file changed, 4 deletions(-)

diff --git a/net/9p/client.c b/net/9p/client.c
index 09f1ec589b80..eb42bbb72f52 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -1617,10 +1617,6 @@ p9_client_read_once(struct p9_fid *fid, u64 offset, struct iov_iter *to,
}

p9_debug(P9_DEBUG_9P, "<<< RREAD count %d\n", count);
- if (!count) {
- p9_tag_remove(clnt, req);
- return 0;
- }

if (non_zc) {
int n = copy_to_iter(dataptr, count, to);
--
2.30.1