Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1206152

Re: [PATCH] net: Use SK_MEM_QUANTUM as minimum for tcp/udp rmem/wmem

Show all headers | View raw

On Tue, 2015-08-11 at 21:54 -0700, Calvin Owens wrote:
> Commit 8133534c760d4083 ("net: limit tcp/udp rmem/wmem to
> SOCK_{RCV,SND}BUF_MIN") modified four sysctls to enforce that the values
> written to them are not less than SOCK_MIN_{RCV,SND}BUF.
> 
> That change causes 4096 (or SK_MEM_QUANTUM) to no longer be accepted as
> a valid value for 'min' in tcp_wmem and udp_wmem_min. 4096 has been the
> default for both of those sysctls for a long time, and unfortunately
> seems to be an extremely popular setting. This change breaks a large
> number of sysctl configurations at FB.
> 
> That commit referred to b1cb59cf2efe7971 ("net: sysctl_net_core: check
> SNDBUF and RCVBUF for min length"), which choose to use the SOCK_MIN
> constants as the lower limits to avoid nasty bugs. But AFAICS, a limit
> of SOCK_MIN_SNDBUF isn't necessary to do that: the BUG_ON cited in the
> commit message seems to have happened because unix_stream_sendmsg()
> expects a minimum of a full page (ie SK_MEM_QUANTUM) and the math broke,
> not because it had less than SOCK_MIN_SNDBUF allocated.
> 
> Nothing seems to assume that it has at least SOCK_MIN_SNDBUF to play
> with, so I think enforcing a minimum of SK_MEM_QUANTUM avoids the sort
> of bugs 8133534c was trying to avoid, and it does so without breaking
> anybody's sysctl configurations.
> 
> Fixes: 8133534c760d4083 ("net: limit tcp/udp rmem/wmem to SOCK_MIN...")
> Signed-off-by: Calvin Owens <calvinowens@fb.com>
> ---

#define SK_MEM_QUANTUM ((int)PAGE_SIZE)

Some arches have PAGE_SIZE = 65536

So your patch might break scripts as well for them.

We should revert 8133534c760d4083.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH] net: Unbreak resetting default values for tcp_wmem/udp_wmem_min Calvin Owens <calvinowens@fb.com> - 2015-08-05 22:30 +0200
  Re: [PATCH] net: Unbreak resetting default values for  tcp_wmem/udp_wmem_min David Miller <davem@davemloft.net> - 2015-08-10 07:50 +0200
    Re: [PATCH] net: Unbreak resetting default values for  tcp_wmem/udp_wmem_min Calvin Owens <calvinowens@fb.com> - 2015-08-11 05:40 +0200
      Re: [PATCH] net: Unbreak resetting default values for  tcp_wmem/udp_wmem_min David Miller <davem@davemloft.net> - 2015-08-11 05:50 +0200
        [PATCH] net: Use SK_MEM_QUANTUM as minimum for tcp/udp rmem/wmem Calvin Owens <calvinowens@fb.com> - 2015-08-12 07:00 +0200
          Re: [PATCH] net: Use SK_MEM_QUANTUM as minimum for tcp/udp rmem/wmem Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-12 16:30 +0200
            Re: [PATCH] net: Use SK_MEM_QUANTUM as minimum for tcp/udp rmem/wmem Sorin Dumitru <sorin@returnze.ro> - 2015-08-12 19:10 +0200
              Re: [PATCH] net: Use SK_MEM_QUANTUM as minimum for tcp/udp rmem/wmem Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-12 19:50 +0200
                Re: [PATCH] net: Use SK_MEM_QUANTUM as minimum for tcp/udp rmem/wmem Calvin Owens <calvinowens@fb.com> - 2015-08-13 23:10 +0200
          [PATCH] Revert "net: limit tcp/udp rmem/wmem to  SOCK_{RCV,SND}BUF_MIN" Calvin Owens <calvinowens@fb.com> - 2015-08-13 23:30 +0200
            Re: [PATCH] Revert "net: limit tcp/udp rmem/wmem to  SOCK_{RCV,SND}BUF_MIN" Eric Dumazet <eric.dumazet@gmail.com> - 2015-08-14 01:00 +0200
            Re: [PATCH] Revert "net: limit tcp/udp rmem/wmem to  SOCK_{RCV,SND}BUF_MIN" David Miller <davem@davemloft.net> - 2015-08-17 21:20 +0200

csiph-web