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Date:   Sun, 28 Feb 2021 19:11:59 +0000
To:     Jakub Kicinski <kuba@kernel.org>
From:   Alexander Lobakin <alobakin@pm.me>
Cc:     Alexander Lobakin <alobakin@pm.me>,
        Pavel Skripkin <paskripkin@gmail.com>, davem@davemloft.net,
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Reply-To: Alexander Lobakin <alobakin@pm.me>
Subject: Re: [PATCH v3] net/core/skbuff: fix passing wrong size to __alloc_skb
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From: Jakub Kicinski <kuba@kernel.org>
Date: Sun, 28 Feb 2021 10:55:52 -0800

> On Sun, 28 Feb 2021 18:14:46 +0000 Alexander Lobakin wrote:
> > > [1] WARNING in __alloc_pages_nodemask+0x5f8/0x730 mm/page_alloc.c:501=
4
> > > Call Trace:
> > >  __alloc_pages include/linux/gfp.h:511 [inline]
> > >  __alloc_pages_node include/linux/gfp.h:524 [inline]
> > >  alloc_pages_node include/linux/gfp.h:538 [inline]
> > >  kmalloc_large_node+0x60/0x110 mm/slub.c:3999
> > >  __kmalloc_node_track_caller+0x319/0x3f0 mm/slub.c:4496
> > >  __kmalloc_reserve net/core/skbuff.c:150 [inline]
> > >  __alloc_skb+0x4e4/0x5a0 net/core/skbuff.c:210
> > >  __netdev_alloc_skb+0x70/0x400 net/core/skbuff.c:446
> > >  netdev_alloc_skb include/linux/skbuff.h:2832 [inline]
> > >  qrtr_endpoint_post+0x84/0x11b0 net/qrtr/qrtr.c:442
> > >  qrtr_tun_write_iter+0x11f/0x1a0 net/qrtr/tun.c:98
> > >  call_write_iter include/linux/fs.h:1901 [inline]
> > >  new_sync_write+0x426/0x650 fs/read_write.c:518
> > >  vfs_write+0x791/0xa30 fs/read_write.c:605
> > >  ksys_write+0x12d/0x250 fs/read_write.c:658
> > >  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
> > >  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >
> > Ah, by the way. Have you tried to seek for the root cause, why
> > a request for such insanely large (at least 4 Mib) skb happens
> > in QRTR? I don't believe it's intended to be like this.
> > Now I feel that silencing this error with early return isn't
> > really correct approach for this.
>
> Right, IIUC Eric suggested we limit the length of the allocation
> to 64KB because that's the max reasonable skb length, and QRTR tun write
> results in generating a single skb. That seems like a good approach.

+1 for explicit capping max skb length to 64K.

Al