From: Chao Yu <chao@kernel.org>
To: Gao Xiang <xiang@kernel.org>, linux-erofs@lists.ozlabs.org
Cc: LKML <linux-kernel@vger.kernel.org>, stable@vger.kernel.org
Subject: Re: [PATCH v2] erofs: fix unsafe pagevec reuse of hooked pclusters
Date: Fri, 5 Nov 2021 12:28:21 +0800 [thread overview]
Message-ID: <1dd327ac-b4c0-6c03-7250-dd8a9be44657@kernel.org> (raw)
In-Reply-To: <20211103182006.4040-1-xiang@kernel.org>
On 2021/11/4 2:20, Gao Xiang wrote:
> There are pclusters in runtime marked with Z_EROFS_PCLUSTER_TAIL
> before actual I/O submission. Thus, the decompression chain can be
> extended if the following pcluster chain hooks such tail pcluster.
>
> As the related comment mentioned, if some page is made of a hooked
> pcluster and another followed pcluster, it can be reused for in-place
> I/O (since I/O should be submitted anyway):
> _______________________________________________________________
> | tail (partial) page | head (partial) page |
> |_____PRIMARY_HOOKED___|____________PRIMARY_FOLLOWED____________|
>
> However, it's by no means safe to reuse as pagevec since if such
> PRIMARY_HOOKED pclusters finally move into bypass chain without I/O
> submission. It's somewhat hard to reproduce with LZ4 and I just found
> it (general protection fault) by ro_fsstressing a LZMA image for long
> time.
>
> I'm going to actively clean up related code together with multi-page
> folio adaption in the next few months. Let's address it directly for
> easier backporting for now.
>
> Call trace for reference:
> z_erofs_decompress_pcluster+0x10a/0x8a0 [erofs]
> z_erofs_decompress_queue.isra.36+0x3c/0x60 [erofs]
> z_erofs_runqueue+0x5f3/0x840 [erofs]
> z_erofs_readahead+0x1e8/0x320 [erofs]
> read_pages+0x91/0x270
> page_cache_ra_unbounded+0x18b/0x240
> filemap_get_pages+0x10a/0x5f0
> filemap_read+0xa9/0x330
> new_sync_read+0x11b/0x1a0
> vfs_read+0xf1/0x190
>
> Fixes: 3883a79abd02 ("staging: erofs: introduce VLE decompression support")
> Cc: <stable@vger.kernel.org> # 4.19+
> Signed-off-by: Gao Xiang <xiang@kernel.org>
Reviewed-by: Chao Yu <chao@kernel.org>
Thanks,
prev parent reply other threads:[~2021-11-05 4:28 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-03 17:49 [PATCH] erofs: fix unsafe pagevec reuse of hooked pclusters Gao Xiang
2021-11-03 18:20 ` [PATCH v2] " Gao Xiang
2021-11-05 4:28 ` Chao Yu [this message]
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