Re: [syzbot] [mm?] WARNING in try_grab_page

[syzbot <syzbot+9b82859567f2e50c123e@syzkaller.appspotmail.com>]

> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

This crash does not have a reproducer. I cannot test it.

>
> lib/scatterlist: Fix error handling in extract_iter_to_sg()
>
> Fix the error handling in extract_iter_to_sg().  Pages need to be unpinned,
> not put, and only if they actually got pinned (which is the case in
> extract_user_to_sg()).
>
> The bug may result in a warning like the following:
>
>   WARNING: CPU: 1 PID: 20384 at mm/gup.c:229 __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:27 [inline]
>   WARNING: CPU: 1 PID: 20384 at mm/gup.c:229 arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline]
>   WARNING: CPU: 1 PID: 20384 at mm/gup.c:229 raw_atomic_add include/linux/atomic/atomic-arch-fallback.h:537 [inline]
>   WARNING: CPU: 1 PID: 20384 at mm/gup.c:229 atomic_add include/linux/atomic/atomic-instrumented.h:105 [inline]
>   WARNING: CPU: 1 PID: 20384 at mm/gup.c:229 try_grab_page+0x108/0x160 mm/gup.c:252
>   ...
>   pc : try_grab_page+0x108/0x160 mm/gup.c:229
>   lr : follow_page_pte+0x174/0x3e4 mm/gup.c:651
>   ...
>   Call trace:
>    __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:27 [inline]
>    arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline]
>    raw_atomic_add include/linux/atomic/atomic-arch-fallback.h:537 [inline]
>    atomic_add include/linux/atomic/atomic-instrumented.h:105 [inline]
>    try_grab_page+0x108/0x160 mm/gup.c:252
>    follow_pmd_mask mm/gup.c:734 [inline]
>    follow_pud_mask mm/gup.c:765 [inline]
>    follow_p4d_mask mm/gup.c:782 [inline]
>    follow_page_mask+0x12c/0x2e4 mm/gup.c:839
>    __get_user_pages+0x174/0x30c mm/gup.c:1217
>    __get_user_pages_locked mm/gup.c:1448 [inline]
>    __gup_longterm_locked+0x94/0x8f4 mm/gup.c:2142
>    internal_get_user_pages_fast+0x970/0xb60 mm/gup.c:3140
>    pin_user_pages_fast+0x4c/0x60 mm/gup.c:3246
>    iov_iter_extract_user_pages lib/iov_iter.c:1768 [inline]
>    iov_iter_extract_pages+0xc8/0x54c lib/iov_iter.c:1831
>    extract_user_to_sg lib/scatterlist.c:1123 [inline]
>    extract_iter_to_sg lib/scatterlist.c:1349 [inline]
>    extract_iter_to_sg+0x26c/0x6fc lib/scatterlist.c:1339
>    hash_sendmsg+0xc0/0x43c crypto/algif_hash.c:117
>    sock_sendmsg_nosec net/socket.c:725 [inline]
>    sock_sendmsg+0x54/0x60 net/socket.c:748
>    ____sys_sendmsg+0x270/0x2ac net/socket.c:2494
>    ___sys_sendmsg+0x80/0xdc net/socket.c:2548
>    __sys_sendmsg+0x68/0xc4 net/socket.c:2577
>    __do_sys_sendmsg net/socket.c:2586 [inline]
>    __se_sys_sendmsg net/socket.c:2584 [inline]
>    __arm64_sys_sendmsg+0x24/0x30 net/socket.c:2584
>    __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
>    invoke_syscall+0x48/0x114 arch/arm64/kernel/syscall.c:52
>    el0_svc_common.constprop.0+0x44/0xe4 arch/arm64/kernel/syscall.c:142
>    do_el0_svc+0x38/0xa4 arch/arm64/kernel/syscall.c:191
>    el0_svc+0x2c/0xb0 arch/arm64/kernel/entry-common.c:647
>    el0t_64_sync_handler+0xc0/0xc4 arch/arm64/kernel/entry-common.c:665
>    el0t_64_sync+0x19c/0x1a0 arch/arm64/kernel/entry.S:591
>
> Fixes: 018584697533 ("netfs: Add a function to extract an iterator into a scatterlist")
> Reported-by: syzbot+9b82859567f2e50c123e@syzkaller.appspotmail.com
> Link: https://lore.kernel.org/linux-mm/000000000000273d0105ff97bf56@google.com/
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Sven Schnelle <svens@linux.ibm.com>
> cc: akpm@linux-foundation.org
> cc: Herbert Xu <herbert@gondor.apana.org.au>
> cc: "David S. Miller" <davem@davemloft.net>
> cc: Jeff Layton <jlayton@kernel.org>
> cc: Steve French <sfrench@samba.org>
> cc: Shyam Prasad N <nspmangalore@gmail.com>
> cc: Rohith Surabattula <rohiths.msft@gmail.com>
> cc: Jens Axboe <axboe@kernel.dk>
> cc: Herbert Xu <herbert@gondor.apana.org.au>
> cc: "David S. Miller" <davem@davemloft.net>
> cc: Eric Dumazet <edumazet@google.com>
> cc: Jakub Kicinski <kuba@kernel.org>
> cc: Paolo Abeni <pabeni@redhat.com>
> cc: Matthew Wilcox <willy@infradead.org>
> cc: linux-mm@kvack.org
> cc: linux-crypto@vger.kernel.org
> cc: linux-cachefs@redhat.com
> cc: linux-cifs@vger.kernel.org
> cc: linux-fsdevel@vger.kernel.org
> cc: netdev@vger.kernel.org
> ---
>  lib/scatterlist.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> index e86231a44c3d..c65566b4dc66 100644
> --- a/lib/scatterlist.c
> +++ b/lib/scatterlist.c
> @@ -1148,7 +1148,7 @@ static ssize_t extract_user_to_sg(struct iov_iter *iter,
>  
>  failed:
>  	while (sgtable->nents > sgtable->orig_nents)
> -		put_page(sg_page(&sgtable->sgl[--sgtable->nents]));
> +		unpin_user_page(sg_page(&sgtable->sgl[--sgtable->nents]));
>  	return res;
>  }
>