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Fri, 9 Feb 2024 15:52:12 -0800 From: Jim Harris To: Bjorn Helgaas , "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Leon Romanovsky , "Jason Gunthorpe" , Alex Williamson , "pierre.cregut@orange.com" Subject: [PATCH v2 1/2] PCI/IOV: Revert "PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes" Thread-Topic: [PATCH v2 1/2] PCI/IOV: Revert "PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes" Thread-Index: AQHaW7MAtwi2xwjfZkaUZDAOVEJQAw== Date: Fri, 9 Feb 2024 23:52:12 +0000 Message-ID: <170752273224.1693615.11371097645648272257.stgit@bgt-140510-bm01.eng.stellus.in> In-Reply-To: <170752254154.1693615.9176696143128338408.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: <89791AD5EB1C934187241FFFDADB64F6@ssi.samsung.com> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CFilter-Loop: Reflected X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrGKsWRmVeSWpSXmKPExsWy7djXc7prdx1LNfg6Wdni2/8eNoslTRkW V/7tYbTYtOEJi8XlXXPYLM7OO85msf7rezYHdo8Fm0o9epvfsXm0PDvJ5vF+31U2j8+b5AJY o7hsUlJzMstSi/TtErgymmbsYSnYJlBxe3EDewNjg0AXIyeHhICJxMSnRxlBbCGBlYwSC3qU IexWJomLr4Ngal427GPtYuQCiq9hlNh9YxorRNFHRol/5+0gEksZJSb397KDJNgENCV+XVnD BJIQEbjKJDF59QdmkISwQKLEjeb3LCC2iECaxLXTlxghbD2JR/+fgtksAioS/26uAavnFYiR 2PPxLROIzQlkv+vbBBZnFBCT+H5qDVicWUBc4taT+UwQpwpKLJq9hxnCFpP4t+shG4StKHH/ +0ug4ziA6jUl1u/Sh2i1k3gxdx8bhK0oMaX7ITvEWkGJkzOfsEC0SkocXHGDBeQXCYEzHBLT Xn5mhUi4SLw8vYcdwpaWuHp9KtTebImV6zuYQHZJCBRINByBhqK1xMI/66FO5pP4++sR4wRG 5VlIPpiFcN0sJNfNQnLdLCTXLWBkXcUoXlpcnJueWmyYl1quV5yYW1yal66XnJ+7iRGYlE7/ O5y7g3HHrY96hxiZOBgPMUpwMCuJ8IYsOZIqxJuSWFmVWpQfX1Sak1p8iFGag0VJnNfQ9mSy kEB6YklqdmpqQWoRTJaJg1OqgclJ++PdVTMvKqUGN+qcm60vt7316E/914bbYzbu3/T/N4fb kzcKmskGc+tKm5PutIifbHcrnGcg9MDJVeZ0w6Sp500kxEKzVsxQmPgrzHd6UuubvZOOrp2U Ktz/Sr+i/+LbxRV3WGtXS60qk5olfOrn+u9vM7vX1oqsqjx4etYUFS0Fq5nv7V+kbr/8QtTn 4nGJ5WU5f8SP7f7eucHm1fuV7C5nP7mXCcp8PngvzIT7XRb/tsY5tnZvDDtuRC8X0bql8m/e xxPTuOflvlL9edZ7ocyczmfH4m5uXj35b+B34TvzElacfih4mKPw1SenIzXft13T5F3TvK9k 5g7R4rp/z9XkVqb8Pldlf09w1eMEOyWW4oxEQy3mouJEANMPk6i5AwAA X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrNIsWRmVeSWpSXmKPExsWS2cDsrLt217FUg2e7eS2+/e9hs1jSlGFx 5d8eRotNG56wWFzeNYfN4uy842wW67++Z3Ng91iwqdSjt/kdm0fLs5NsHu/3XWXz+LxJLoA1 issmJTUnsyy1SN8ugSujacYeloJtAhW3FzewNzA2CHQxcnJICJhIvGzYx9rFyMUhJLCKUWLF lbUsEM5HRoklS5dAZZYySiw8+4kNpIVNQFPi15U1TCAJEYGrTBKTV39gBkkICyRKXL08jxHE FhFIk7h2+hKUrSfx6P9TMJtFQEXi3801YPW8AjESez6+ZQKxhQSiJeZPnMwOYnMCxd/1bQKr YRQQk/h+ag1YDbOAuMStJ/OZIO4WkFiy5zwzhC0q8fLxP1YIW1Hi/veXQHM4gOo1Jdbv0odo tZN4MXcfG4StKDGl+yE7xAmCEidnPmGBaJWUOLjiBssERvFZSLbNQpg0C8mkWUgmzUIyaQEj 6ypG8dLi4tz0imLDvNRyveLE3OLSvHS95PzcTYzA+D3973DkDsajtz7qHWJk4mA8xCjBwawk whuy5EiqEG9KYmVValF+fFFpTmrxIUZpDhYlcd67DzRShQTSE0tSs1NTC1KLYLJMHJxSDUwh Bi/tDFxrHTed+iEn92TBBPt+U2WORczPtqw6+P3f4yCjHetUgiSvzLz38cHu1J7lvUveCPb8 XbpWft7iWQElPFEPWQPrFv6YdrfRsejP1Dm3801N/I0cylOrW1Nl3f6lLK2YZnLkyeKQtO/b FpnuCwqst04uVTr76oH1kkO/7V/HRcmo+dlGum27lbDtZ1ce7web8xtjSs7t3nVg3b1nRs9f XU+WbXNssit4pPBtr+/sUC6NzI8pSfpqkzZeWnl3xg/TuaZOru3d4dnlsZwXF9TXSZyJTfnf NLEi+/gsj5N7L9/rWvm0+/JL371hVq0pLVvvGO6slT/oKiwhstZtz7E9308ayq+4nBNsJ1Ko xFKckWioxVxUnAgAc2HpCE4DAAA= X-CMS-MailID: 20240209235213uscas1p2e8de2bdf05e6e7cba51bd41ddb42a8e4 CMS-TYPE: 301P X-CMS-RootMailID: 20240209235213uscas1p2e8de2bdf05e6e7cba51bd41ddb42a8e4 References: <170752254154.1693615.9176696143128338408.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); } /*