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R. Silva" , "linux-kernel@vger.kernel.org" , "linux-cxl@vger.kernel.org" , "linux-hardening@vger.kernel.org" , Leon Romanovsky , "Jason Gunthorpe" , Alex Williamson , "pierre.cregut@orange.com" Subject: [PATCH v3 1/2] PCI/IOV: Revert "PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes" Thread-Topic: [PATCH v3 1/2] PCI/IOV: Revert "PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes" Thread-Index: AQHaX5l/Y5bHR2DvZ0+eeI1J9u0GaA== Date: Wed, 14 Feb 2024 22:59:42 +0000 Message-ID: <170795158249.2393.6069168125066679172.stgit@bgt-140510-bm01.eng.stellus.in> In-Reply-To: <170795147587.2393.15577527626926144858.stgit@bgt-140510-bm01.eng.stellus.in> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: Content-ID: <84A3C9C8FC63C94C827BCF517FA70757@ssi.samsung.com> Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CFilter-Loop: Reflected X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFnrJKsWRmVeSWpSXmKPExsWy7djX87oPXM+mGjz+yWnx7X8Pm8XdxxfY LKZPvcBoceJmI5vF6ptrGC1+XZzGarH/6XMWiyv/9jBarFp4jc3iTHeuxaYNT1gszs86xWIx b/1PRovLu+awWaz/+p7N4taEY0wOAh6zGy6yeLQcecvqsXjPSyaPTas62Tx6m9+xebQ8O8nm 8X7fVTaPqbPrPT5vkgvgjOKySUnNySxLLdK3S+DKaJqxh6Vgm0DF7cUN7A2MDQJdjJwcEgIm Ev2nd7F0MXJxCAmsZJS4fPAxlNPKJDF/8mQ2mKrNKydAJdYwSix9e58NwvnEKNF67AZUZhmj xN+fbxhBWtgENCV+XVnDBJIQEfjIKtG3Ywo7SEJYIFHi0LdbrCC2iECaxPreHhYIW0/i1/2l YM0sAqoS35r6wGp4BSIkdp76BRbnFIiS+P35BZjNKCAm8f0UyAJODmYBcYlbT+YzQdwqKLFo 9h5mCFtM4t+uh1A/KErc//4S6AYOoHpNifW79CFa7SQm3bnABmErSkzpfsgOsVZQ4uTMJywQ rZISB1fcgLJXc0p0H1aBsF0kLs1ayQhhS0v8vbsM6oRsiZXrO5hAVkkIFEg0HAmCCFtLLPyz HupiPom/vx4xTmBUnoXkgVkIx81CctwsJMfNQnLcAkbWVYzipcXFuempxcZ5qeV6xYm5xaV5 6XrJ+bmbGIGp8fS/wwU7GG/d+qh3iJGJg/EQowQHs5II76TeM6lCvCmJlVWpRfnxRaU5qcWH GKU5WJTEeQ1tTyYLCaQnlqRmp6YWpBbBZJk4OKUamBp89hreC+ZIWH4y1NzuVtW3oyKBujOj VF69Xskq4vvtWTufmFR6wCrLEE736UeNHm68/Leg79uVv6+atS88FJ7NcU2467wuu+7yp+ud trl+yzmcP5/t+sWdRounzw7OnXfxU6oLT2JjTVfQ9s5fJ40Sru5QqO3MdjvDbRReszg+6Ero 4gkBkQten76436/CyMwmsMezY85m76hYLfZ7n3XD/Xtk8+bmHtUXCrxwjeHbrhsrFySu7/9X FvCvNOn5Aq2/S4PeM17ZU9mz4/21iTNuRcyTnq3ufOJjqfSRWfcKsz7+nZb1M3itsN31ozKT xasMLv62PSZaHDHPaNqSxubKu6/UXO3C+t+GzLstsEuJpTgj0VCLuag4EQCTTbim/AMAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA02Se0hTYRjG+XbOjsfR8mtafi2QGnQxSLtRH2QShXGC1G6kGVEjT9NypjtO K7rMC0aXxRTndJbLsqglaMssbRVTy0ulRpblNA1nTcIsLcsZmvMU+d/ve5/3ed7nj48mJKOk lI6NT2JV8fI4GSUiYzXE+iVdIS/Ypb8s/nh4/DyFO3taKGzQtwBc/y6VwrfelQDsepkrxI97 P5G4dcwKsLnoDYWfn1NiS5mDxM3GRhIXlo4A/KrqIoVLfwxQuF33VLAOMgWalySTUdsvZK5a +wSMxXyGYrTpXygm42MDxQw8ek0x+oJTzJDFb4tnlCgomo2LTWZVgcH7RDFpeVYyoQIesV/V eGiABp4FnjSCK9GdmzryLBDREmgG6N5vi4B/DALkGO/+q1wHKNdm8HBbKOiPXK0lk1s+8JsQ DXXrJwVvKEdaQ63AzT7wACrVnid5DkCurmvAzSScj4bTLgjdLIaRqLLRNTGnJy7sQrq2JPfY E0ah0SHn5DqAs9DPxpLJSAL6onaHScDXhqjY2kzwPBP19YwJeZ6Hun72ebgjiYmepVWBvDUY ZXe0UDzPQznnPnjwDWaghnwHyVtnI9uNt6QO+BqnXDP+TzJOSTJOSTJOSboMhGbgq+Y4peII tzyeTQng5EpOHa8I2H9YaQET/+PZWM3u+8De/i2gGghoUA0QTch8xNna56xEHC0/eoxVHd6r UsexXDWYQ5MyX3Fn9yJWAhXyJPYQyyawqn+qgPaUagSrDaZcvwjTgAomZ9qcm6TNpuCycOvn K9kiadHn9qaYus2XfqH09LvRI6GSjsf5tbO5zDQdQSt2yZ7FnihuXiPcFvJBvGFRXOV0KUgp rG+ojbQ1zNp+Kef019bGrMvKCLF9Ey0ThTrrF/qZThlGVuC8GrV/mD61TWlpWrAjTIiZ+akV q7Tvd/annJ5W931r75or906aiwtW3tl4ZnC3s3AwMfFVLqpQv+6vr5AQYu+UtgVeMtLVUZ7A 7omwN4mCJHnbHxRFMsezjFu8uqwvbJu33aZ7l3uVrw46mpisfNP5RD8t1DXXKcl6WLk02Xmx hwzvPvhW4dhnX4tD+tZXyUguRr5sMaHi5H8Ami8tP44DAAA= X-CMS-MailID: 20240214225943uscas1p21ffa8b362bac11379168b83e42159160 CMS-TYPE: 301P X-CMS-RootMailID: 20240214225943uscas1p21ffa8b362bac11379168b83e42159160 References: <170795147587.2393.15577527626926144858.stgit@bgt-140510-bm01.eng.stellus.in> If an SR-IOV enabled device is held by vfio, and the device is removed, vfio will hold device lock and notify userspace of the removal. If userspace reads the sriov_numvfs sysfs entry, that thread will be blocked since sriov_numvfs_show() also tries to acquire the device lock. If that same thread is responsible for releasing the device to vfio, it results in a deadlock. The proper way to detect a change to the num_VFs value is to listen for a sysfs event, not to add a device_lock() on the attribute _show() in the kernel. This reverts commit 35ff867b76576e32f34c698ccd11343f7d616204. Revert had a small conflict, the sprintf() is now changed to sysfs_emit(). Link: https://lore.kernel.org/linux-pci/ZXJI5+f8bUelVXqu@ubuntu/ Suggested-by: Leon Romanovsky Reviewed-by: Leon Romanovsky Signed-off-by: Jim Harris --- drivers/pci/iov.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c index aaa33e8dc4c9..0ca20cd518d5 100644 --- a/drivers/pci/iov.c +++ b/drivers/pci/iov.c @@ -395,14 +395,8 @@ static ssize_t sriov_numvfs_show(struct device *dev, char *buf) { struct pci_dev *pdev = to_pci_dev(dev); - u16 num_vfs; - - /* Serialize vs sriov_numvfs_store() so readers see valid num_VFs */ - device_lock(&pdev->dev); - num_vfs = pdev->sriov->num_VFs; - device_unlock(&pdev->dev); - return sysfs_emit(buf, "%u\n", num_vfs); + return sysfs_emit(buf, "%u\n", pdev->sriov->num_VFs); } /*