From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.nokia.com ([192.100.122.230] helo=mgw-mx03.nokia.com) by bombadil.infradead.org with esmtps (Exim 4.69 #1 (Red Hat Linux)) id 1M1afZ-0000Id-9z for linux-mtd@lists.infradead.org; Wed, 06 May 2009 06:32:00 +0000 Subject: Re: [PATCH] [UBI] [1/3] ubi notifications API From: Artem Bityutskiy To: dpervushin@embeddedalley.com In-Reply-To: <1241018978.20184.33.camel@hp.diimka.lan> References: <1241018978.20184.33.camel@hp.diimka.lan> Content-Type: text/plain; charset="UTF-8" Date: Wed, 06 May 2009 09:31:42 +0300 Message-Id: <1241591502.3760.44.camel@localhost.localdomain> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Cc: linux-mtd@lists.infradead.org Reply-To: dedekind@infradead.org List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2009-04-29 at 19:29 +0400, dmitry pervushin wrote: > UBI volume notifications are intended to create the API to get clients > notified about volume creation/deletion, renaming and changing(actually, > resizing). A client can subscribe to these notifications using > ubi_volume_register and cancel the subscription using > ubi_volume_unregister. When UBI volume change occurs, the atomic > notifier will be called. Client also can request "added" event on all > volumes that existed before client subscribed to the notifications. > > Using notifications instead of calling functions ubi_gluebi_xxx allows > MTD emulation layer to be more flexible; say, now is it possible to > build it as a module and load/unload it on demand. > > Thanks Artem Bityutskiy for reviewing the patch and many very valuable > comments. > > Signed-off-by: Dmitry Pervushin > --- > drivers/mtd/ubi/build.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++-- > drivers/mtd/ubi/cdev.c | 2 + > drivers/mtd/ubi/kapi.c | 46 +++++++++++++++++++++++++++ > drivers/mtd/ubi/ubi.h | 24 ++++++++++++++ > drivers/mtd/ubi/vmt.c | 7 ++++ > include/linux/mtd/ubi.h | 35 +++++++++++++++++++++ > 6 files changed, 191 insertions(+), 3 deletions(-) > > Index: linux-2.6-arm/drivers/mtd/ubi/build.c > =================================================================== > --- linux-2.6-arm.orig/drivers/mtd/ubi/build.c > +++ linux-2.6-arm/drivers/mtd/ubi/build.c > @@ -122,6 +122,76 @@ static struct device_attribute dev_mtd_n > __ATTR(mtd_num, S_IRUGO, dev_attribute_show, NULL); > > /** > + * ubi_enum_volumes - "enumerate" volumes. > + * @ntype: notification type to send (%UBI_VOLUME_ADDED, etc) > + * @ubi: UBI device description object > + * @nb: notifier to be called or %NULL to send to system-wide notification > + * > + * This function walks all volumes of UBI device @ubi and sends the > + * notification specified by @ntype. Returns number of sent notifications. > + */ > +int ubi_enum_volumes(int ntype, struct ubi_device *ubi, > + struct notifier_block *nb) > +{ > + struct ubi_volume_notification nt; > + int i, count = 0; > + > + nt.ubi_num = ubi->ubi_num; > + > + spin_lock(&ubi->volumes_lock); > + for (i = 0; i < ubi->vtbl_slots; i++) { > + if (!ubi->volumes[i]) > + continue; > + nt.vol_id = ubi->volumes[i]->vol_id; > + get_device(&ubi->volumes[i]->dev); > + ubi->volumes[i]->ref_count += 1; > + spin_unlock(&ubi->volumes_lock); > + if (nb) > + nb->notifier_call(nb, ntype, &nt); > + else > + blocking_notifier_call_chain(&ubi_notifiers, > + ntype, &nt); > + count++; > + spin_lock(&ubi->volumes_lock); > + ubi->volumes[i]->ref_count -= 1; > + put_device(&ubi->volumes[i]->dev); > + } > + spin_unlock(&ubi->volumes_lock); > + > + return count; > +} > + > +/** > + * ubi_enum_all_volumes - enumerate all existing volumes and send notification. > + * @ntype: notification type to send (%UBI_VOLUME_ADDED, etc) > + * @nb: notifier to be called, or %NULL to send to system-wide notification > + * > + * This function walks all UBI devices and all volumes on the device, and sends > + * the notification specified by @ntype. Returns number of sent notifications. > + */ > +int ubi_enum_all_volumes(int ntype, struct notifier_block *nb) > +{ > + struct ubi_device *ubi; > + int i, count = 0; > + > + spin_lock(&ubi_devices_lock); > + for (i = 0; i < UBI_MAX_DEVICES; i++) { > + ubi = ubi_devices[i]; > + if (!ubi) > + continue; > + ubi->ref_count += 1; > + get_device(&ubi->dev); > + spin_unlock(&ubi_devices_lock); > + count += ubi_enum_volumes(ntype, ubi, nb); > + spin_lock(&ubi_devices_lock); > + put_device(&ubi->dev); > + ubi->ref_count -= 1; > + } > + spin_unlock(&ubi_devices_lock); > + return count; > +} The locking is still screwed. I do not think the code will work when enumeration races with volume creation/deletion etc, or when it races with device detach. And I do not think the subscribers will get sensible sequence of events in this case. The right solution would be to re-work locking, and use mutexes instead of this (not very sane) "exlusive" flag. Roughly, I believe there should be 2 mutexes: 1. global "devices mutex" - locked when whole MTD device is attached/detached. 2. per-UBI device "device mutex" - locked when volumes belonging to this device are created/removed/resized/renamed. And this "exlusive" open mode should go away. I'll see what I can do. I'll try to prepare new locking for you. Will let you know. -- Best regards, Artem Bityutskiy (Битюцкий Артём)