From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55949) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dPmml-0007bJ-M3 for qemu-devel@nongnu.org; Tue, 27 Jun 2017 05:27:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dPmmh-0004oH-OA for qemu-devel@nongnu.org; Tue, 27 Jun 2017 05:27:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47574) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dPmmh-0004o6-I2 for qemu-devel@nongnu.org; Tue, 27 Jun 2017 05:27:47 -0400 References: <20170605123908.18777-1-pbonzini@redhat.com> <20170605123908.18777-17-pbonzini@redhat.com> <37960694-8f25-8201-5f17-e59c3ee67e90@redhat.com> From: Paolo Bonzini Message-ID: Date: Tue, 27 Jun 2017 11:27:42 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org Cc: famz@redhat.com On 27/06/2017 11:07, Vladimir Sementsov-Ogievskiy wrote: > 26.06.2017 19:54, Paolo Bonzini wrote: >> >> On 26/06/2017 18:07, Vladimir Sementsov-Ogievskiy wrote: >>> HI! >>> >>> One question here, should not 'bdrv_undo_clear_dirty_bitmap' be under >>> lock too? >> Any call to dirty bitmap functions between bdrv_clear_dirty_bitmap and >> bdrv_undo_clear_dirty_bitmap is problematic anyway, so >> bdrv_clear_dirty_bitmap really only needs the lock in the !out case; >> bdrv_undo_clear_dirty_bitmap is only called when out != NULL. >> >> However, I agree it would be cleaner to add the lock there, too. > > Also, you've added comment "Called with BQL taken" both to functions > that calls bdrv_dirty_bitmaps_lock and that do not... What is BQL? It's the "big QEMU lock", also known as "iothread lock". The locking policy is documented in block_int.h: /* Writing to the list requires the BQL _and_ the dirty_bitmap_mutex. * Reading from the list can be done with either the BQL or the * dirty_bitmap_mutex. Modifying a bitmap only requires * dirty_bitmap_mutex. */ QemuMutex dirty_bitmap_mutex; QLIST_HEAD(, BdrvDirtyBitmap) dirty_bitmaps; and the comments in block/dirty-bitmap.c reflect the above comment. Paolo