[v2] net: 9p: advance iov on empty read
diff mbox series

Message ID 20210302171932.28e86231@xhacker.debian
State Accepted
Commit d65614a01d24704b016635abf5cc028a54e45a62
Headers show
Series
  • [v2] net: 9p: advance iov on empty read
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Commit Message

Jisheng Zhang March 2, 2021, 9:19 a.m. UTC
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>
---
Since v1:
 - reword the commit msg
 - fix the issue by removing exception for 0 code path, thank Dominique!

 net/9p/client.c | 4 ----
 1 file changed, 4 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org March 4, 2021, 1:10 a.m. UTC | #1
Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Tue, 2 Mar 2021 17:19:32 +0800 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [v2] net: 9p: advance iov on empty read
    https://git.kernel.org/netdev/net/c/d65614a01d24

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
Dominique Martinet March 4, 2021, 3:01 a.m. UTC | #2
patchwork-bot+netdevbpf@kernel.org wrote on Thu, Mar 04, 2021 at 01:10:07AM +0000:
> This patch was applied to netdev/net.git

thanks for taking the patch, I didn't take the time to reply yesterday
after my bisect finally finished.

I've got the culprit now, could you add the following?

Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
(or reviewed-by/tested-by, or just leave it out I'm not fussy)
Fixes: cf03f316ad20 ("fs: 9p: add generic splice_read file operations")
Cc: stable@vger.kernel.org # v5.11


Cheers,

Patch
diff mbox series

diff --git a/net/9p/client.c b/net/9p/client.c
index 4f62f299da0c..0a9019da18f3 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -1623,10 +1623,6 @@  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);