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[85.229.41.228]) by smtp.gmail.com with ESMTPSA id w23-20020a19c517000000b004b5701b5337sm1843649lfe.104.2022.12.21.05.34.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Dec 2022 05:34:30 -0800 (PST) Date: Wed, 21 Dec 2022 14:34:28 +0100 From: Anders Roxell To: Tejun Heo Cc: Ian Kent , Greg Kroah-Hartman , Minchan Kim , Eric Sandeen , Al Viro , Rick Lindsley , David Howells , Miklos Szeredi , Carlos Maiolino , linux-fsdevel , Kernel Mailing List , elver@google.com, arnd@arndb.de Subject: Re: [PATCH 1/2] kernfs: dont take i_lock on inode attr read Message-ID: <20221221133428.GE69385@mutt> References: <166606025456.13363.3829702374064563472.stgit@donald.themaw.net> <166606036215.13363.1288735296954908554.stgit@donald.themaw.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2022-10-31 12:30, Tejun Heo wrote: > On Tue, Oct 18, 2022 at 10:32:42AM +0800, Ian Kent wrote: > > The kernfs write lock is held when the kernfs node inode attributes > > are updated. Therefore, when either kernfs_iop_getattr() or > > kernfs_iop_permission() are called the kernfs node inode attributes > > won't change. > > > > Consequently concurrent kernfs_refresh_inode() calls always copy the > > same values from the kernfs node. > > > > So there's no need to take the inode i_lock to get consistent values > > for generic_fillattr() and generic_permission(), the kernfs read lock > > is sufficient. > > > > Signed-off-by: Ian Kent > > Acked-by: Tejun Heo Hi, Building an allmodconfig arm64 kernel on yesterdays next-20221220 and booting that in qemu I see the following "BUG: KCSAN: data-race in set_nlink / set_nlink". ================================================================== [ 1540.388669][ T123] BUG: KCSAN: data-race in set_nlink / set_nlink [ 1540.392779][ T123] [ 1540.394302][ T123] write to 0xffff00000adcc3e4 of 4 bytes by task 126 on cpu 0: [ 1540.398828][ T123] set_nlink (/home/anders/src/kernel/next/fs/inode.c:371) [ 1540.401609][ T123] kernfs_refresh_inode (/home/anders/src/kernel/next/fs/kernfs/inode.c:181) [ 1540.404925][ T123] kernfs_iop_getattr (/home/anders/src/kernel/next/fs/kernfs/inode.c:194) [ 1540.408088][ T123] vfs_getattr_nosec (/home/anders/src/kernel/next/fs/stat.c:133) [ 1540.411334][ T123] vfs_statx (/home/anders/src/kernel/next/fs/stat.c:170) [ 1540.414224][ T123] vfs_fstatat (/home/anders/src/kernel/next/fs/stat.c:276) [ 1540.417166][ T123] __do_sys_newfstatat (/home/anders/src/kernel/next/fs/stat.c:446) [ 1540.420539][ T123] __arm64_sys_newfstatat (/home/anders/src/kernel/next/fs/stat.c:440 /home/anders/src/kernel/next/fs/stat.c:440) [ 1540.424003][ T123] el0_svc_common.constprop.0 (/home/anders/src/kernel/next/arch/arm64/kernel/syscall.c:38 /home/anders/src/kernel/next/arch/arm64/kernel/syscall.c:52 /home/anders/src/kernel/next/arch/arm64/kernel/syscall.c:142) [ 1540.427648][ T123] do_el0_svc (/home/anders/src/kernel/next/arch/arm64/kernel/syscall.c:197) [ 1540.430378][ T123] el0_svc (/home/anders/src/kernel/next/arch/arm64/kernel/entry-common.c:133 /home/anders/src/kernel/next/arch/arm64/kernel/entry-common.c:142 /home/anders/src/kernel/next/arch/arm64/kernel/entry-common.c:638) [ 1540.433053][ T123] el0t_64_sync_handler (/home/anders/src/kernel/next/arch/arm64/kernel/entry-common.c:656) [ 1540.436421][ T123] el0t_64_sync (/home/anders/src/kernel/next/arch/arm64/kernel/entry.S:584) [ 1540.439303][ T123] [ 1540.440828][ T123] 1 lock held by systemd-udevd/126: [ 1540.444055][ T123] #0: ffff00000609b960 (&root->kernfs_rwsem){++++}-{3:3}, at: kernfs_iop_getattr (/home/anders/src/kernel/next/fs/kernfs/inode.c:193) [ 1540.450699][ T123] irq event stamp: 185034 [ 1540.453373][ T123] hardirqs last enabled at (185034): seqcount_lockdep_reader_access (/home/anders/src/kernel/next/mm/page_alloc.c:5302) [ 1540.460087][ T123] hardirqs last disabled at (185033): seqcount_lockdep_reader_access (/home/anders/src/kernel/next/include/linux/seqlock.h:103 (discriminator 4)) [ 1540.466686][ T123] softirqs last enabled at (185001): fpsimd_restore_current_state (/home/anders/src/kernel/next/arch/arm64/kernel/fpsimd.c:264 /home/anders/src/kernel/next/arch/arm64/kernel/fpsimd.c:1780) [ 1540.473310][ T123] softirqs last disabled at (184999): fpsimd_restore_current_state (/home/anders/src/kernel/next/include/linux/bottom_half.h:20 /home/anders/src/kernel/next/arch/arm64/kernel/fpsimd.c:242 /home/anders/src/kernel/next/arch/arm64/kernel/fpsimd.c:1773) [ 1540.479872][ T123] [ 1540.481406][ T123] read to 0xffff00000adcc3e4 of 4 bytes by task 123 on cpu 0: [ 1540.485893][ T123] set_nlink (/home/anders/src/kernel/next/fs/inode.c:368) [ 1540.488663][ T123] kernfs_refresh_inode (/home/anders/src/kernel/next/fs/kernfs/inode.c:181) [ 1540.491961][ T123] kernfs_iop_permission (/home/anders/src/kernel/next/fs/kernfs/inode.c:290) [ 1540.495260][ T123] inode_permission (/home/anders/src/kernel/next/fs/namei.c:458 /home/anders/src/kernel/next/fs/namei.c:525) [ 1540.498450][ T123] link_path_walk (/home/anders/src/kernel/next/fs/namei.c:1715 /home/anders/src/kernel/next/fs/namei.c:2262) [ 1540.501552][ T123] path_lookupat (/home/anders/src/kernel/next/fs/namei.c:2473 (discriminator 2)) [ 1540.504592][ T123] filename_lookup (/home/anders/src/kernel/next/fs/namei.c:2503) [ 1540.507740][ T123] user_path_at_empty (/home/anders/src/kernel/next/fs/namei.c:2876) [ 1540.511010][ T123] do_readlinkat (/home/anders/src/kernel/next/fs/stat.c:477) [ 1540.514097][ T123] __arm64_sys_readlinkat (/home/anders/src/kernel/next/fs/stat.c:504 /home/anders/src/kernel/next/fs/stat.c:501 /home/anders/src/kernel/next/fs/stat.c:501) [ 1540.517598][ T123] el0_svc_common.constprop.0 (/home/anders/src/kernel/next/arch/arm64/kernel/syscall.c:38 /home/anders/src/kernel/next/arch/arm64/kernel/syscall.c:52 /home/anders/src/kernel/next/arch/arm64/kernel/syscall.c:142) [ 1540.521319][ T123] do_el0_svc (/home/anders/src/kernel/next/arch/arm64/kernel/syscall.c:197) [ 1540.524125][ T123] el0_svc (/home/anders/src/kernel/next/arch/arm64/kernel/entry-common.c:133 /home/anders/src/kernel/next/arch/arm64/kernel/entry-common.c:142 /home/anders/src/kernel/next/arch/arm64/kernel/entry-common.c:638) [ 1540.526795][ T123] el0t_64_sync_handler (/home/anders/src/kernel/next/arch/arm64/kernel/entry-common.c:656) [ 1540.530224][ T123] el0t_64_sync (/home/anders/src/kernel/next/arch/arm64/kernel/entry.S:584) [ 1540.533176][ T123] [ 1540.534710][ T123] 1 lock held by systemd-udevd/123: [ 1540.537977][ T123] #0: ffff00000609b960 (&root->kernfs_rwsem){++++}-{3:3}, at: kernfs_iop_permission (/home/anders/src/kernel/next/fs/kernfs/inode.c:289) [ 1540.544892][ T123] irq event stamp: 216564 [ 1540.547603][ T123] hardirqs last enabled at (216564): seqcount_lockdep_reader_access (/home/anders/src/kernel/next/mm/page_alloc.c:5302) [ 1540.554368][ T123] hardirqs last disabled at (216563): seqcount_lockdep_reader_access (/home/anders/src/kernel/next/include/linux/seqlock.h:103 (discriminator 4)) [ 1540.561107][ T123] softirqs last enabled at (216533): fpsimd_restore_current_state (/home/anders/src/kernel/next/arch/arm64/kernel/fpsimd.c:264 /home/anders/src/kernel/next/arch/arm64/kernel/fpsimd.c:1780) [ 1540.567833][ T123] softirqs last disabled at (216531): fpsimd_restore_current_state (/home/anders/src/kernel/next/include/linux/bottom_half.h:20 /home/anders/src/kernel/next/arch/arm64/kernel/fpsimd.c:242 /home/anders/src/kernel/next/arch/arm64/kernel/fpsimd.c:1773) [ 1540.574496][ T123] [ 1540.576050][ T123] Reported by Kernel Concurrency Sanitizer on: [ 1540.587925][ T123] Hardware name: linux,dummy-virt (DT) [ 1540.591282][ T123] ================================================================== Reverting this patch I don't see the data race anymore. Cheers, Anders