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d="scan'208";a="2501599" From: Paul Durrant To: Date: Tue, 2 Jul 2019 17:38:39 +0100 Message-ID: <20190702163840.2107-3-paul.durrant@citrix.com> X-Mailer: git-send-email 2.20.1.2.gb21ebb671 In-Reply-To: <20190702163840.2107-1-paul.durrant@citrix.com> References: <20190702163840.2107-1-paul.durrant@citrix.com> MIME-Version: 1.0 Subject: [Xen-devel] [PATCH 2/3] xmalloc: don't evaluate ADD_REGION without holding the pool lock X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Wei Liu , Konrad Rzeszutek Wilk , George Dunlap , Andrew Cooper , Ian Jackson , Tim Deegan , Julien Grall , Paul Durrant , Jan Beulich Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" It's not safe to add a region without holding the lock, but this is exactly what may happen if two threads race entering xmem_pool_alloc() before the init_region is set. This patch instead checks for init_region under lock, drops the lock if it needs to allocate a page, takes the lock, adds the region and then confirms init_region is still unset before pointing it at the newly added region. Thus, it is possible that a race may cause an extra region to be added, but there will be no pool metadata corruption. Signed-off-by: Paul Durrant --- Cc: Andrew Cooper Cc: George Dunlap Cc: Ian Jackson Cc: Jan Beulich Cc: Julien Grall Cc: Konrad Rzeszutek Wilk Cc: Stefano Stabellini Cc: Tim Deegan Cc: Wei Liu --- xen/common/xmalloc_tlsf.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/xen/common/xmalloc_tlsf.c b/xen/common/xmalloc_tlsf.c index 6d889b7bdc..71597c3590 100644 --- a/xen/common/xmalloc_tlsf.c +++ b/xen/common/xmalloc_tlsf.c @@ -380,18 +380,22 @@ void *xmem_pool_alloc(unsigned long size, struct xmem= _pool *pool) int fl, sl; unsigned long tmp_size; =20 + spin_lock(&pool->lock); if ( pool->init_region =3D=3D NULL ) { + spin_unlock(&pool->lock); if ( (region =3D pool->get_mem(pool->init_size)) =3D=3D NULL ) goto out; + spin_lock(&pool->lock); ADD_REGION(region, pool->init_size, pool); - pool->init_region =3D region; + /* Re-check since the lock was dropped */ + if ( pool->init_region =3D=3D NULL ) + pool->init_region =3D region; } =20 size =3D (size < MIN_BLOCK_SIZE) ? MIN_BLOCK_SIZE : ROUNDUP_SIZE(size); /* Rounding up the requested size and calculating fl and sl */ =20 - spin_lock(&pool->lock); retry_find: MAPPING_SEARCH(&size, &fl, &sl); =20 --=20 2.20.1.2.gb21ebb671 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel