From: Chao Yu <yuchao0@huawei.com>
To: Eric Biggers <ebiggers@kernel.org>,
<linux-f2fs-devel@lists.sourceforge.net>
Cc: <linux-fscrypt@vger.kernel.org>
Subject: Re: [PATCH] f2fs: fix deadlock allocating bio_post_read_ctx from mempool
Date: Thu, 2 Jan 2020 16:13:01 +0800 [thread overview]
Message-ID: <883839de-94e7-9c93-388b-9787e3fa76ba@huawei.com> (raw)
In-Reply-To: <20191231181416.47875-1-ebiggers@kernel.org>
On 2020/1/1 2:14, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> Without any form of coordination, any case where multiple allocations
> from the same mempool are needed at a time to make forward progress can
> deadlock under memory pressure.
>
> This is the case for struct bio_post_read_ctx, as one can be allocated
> to decrypt a Merkle tree page during fsverity_verify_bio(), which itself
> is running from a post-read callback for a data bio which has its own
> struct bio_post_read_ctx.
>
> Fix this by freeing first bio_post_read_ctx before calling
> fsverity_verify_bio(). This works because verity (if enabled) is always
> the last post-read step.
>
> This deadlock can be reproduced by trying to read from an encrypted
> verity file after reducing NUM_PREALLOC_POST_READ_CTXS to 1 and patching
> mempool_alloc() to pretend that pool->alloc() always fails.
>
> Note that since NUM_PREALLOC_POST_READ_CTXS is actually 128, to actually
> hit this bug in practice would require reading from lots of encrypted
> verity files at the same time. But it's theoretically possible, as N
> available objects doesn't guarantee forward progress when > N/2 threads
> each need 2 objects at a time.
>
> Fixes: 95ae251fe828 ("f2fs: add fs-verity support")
> Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Thanks,
prev parent reply other threads:[~2020-01-02 8:13 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-31 18:14 [PATCH] f2fs: fix deadlock allocating bio_post_read_ctx from mempool Eric Biggers
2020-01-02 8:13 ` Chao Yu [this message]
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