92 lines
2.7 KiB
Diff
92 lines
2.7 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Brian Behlendorf <behlendorf1@llnl.gov>
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Date: Wed, 11 Jul 2018 15:49:10 -0700
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Subject: [PATCH] Fix zpl_mount() deadlock
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Commit 93b43af10 inadvertently introduced the following scenario which
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can result in a deadlock. This issue was most easily reproduced by
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LXD containers using a ZFS storage backend but should be reproducible
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under any workload which is frequently mounting and unmounting.
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-- THREAD A --
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spa_sync()
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spa_sync_upgrades()
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rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG); <- Waiting on B
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-- THREAD B --
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mount_fs()
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zpl_mount()
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zpl_mount_impl()
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dmu_objset_hold()
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dmu_objset_hold_flags()
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dsl_pool_hold()
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dsl_pool_config_enter()
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rrw_enter(&dp->dp_config_rwlock, RW_READER, tag);
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sget()
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sget_userns()
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grab_super()
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down_write(&s->s_umount); <- Waiting on C
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-- THREAD C --
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cleanup_mnt()
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deactivate_super()
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down_write(&s->s_umount);
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deactivate_locked_super()
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zpl_kill_sb()
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kill_anon_super()
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generic_shutdown_super()
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sync_filesystem()
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zpl_sync_fs()
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zfs_sync()
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zil_commit()
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txg_wait_synced() <- Waiting on A
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Reviewed by: Alek Pinchuk <apinchuk@datto.com>
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Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
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Closes #7598
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Closes #7659
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Closes #7691
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Closes #7693
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Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
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---
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include/sys/zfs_vfsops.h | 1 +
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module/zfs/zpl_super.c | 11 ++++++++++-
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2 files changed, 11 insertions(+), 1 deletion(-)
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diff --git a/include/sys/zfs_vfsops.h b/include/sys/zfs_vfsops.h
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index 2326da42..927153b2 100644
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--- a/include/sys/zfs_vfsops.h
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+++ b/include/sys/zfs_vfsops.h
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@@ -32,6 +32,7 @@
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#include <sys/zil.h>
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#include <sys/sa.h>
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#include <sys/rrwlock.h>
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+#include <sys/dsl_dataset.h>
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#include <sys/zfs_ioctl.h>
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#ifdef __cplusplus
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diff --git a/module/zfs/zpl_super.c b/module/zfs/zpl_super.c
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index fc10271b..5c426b0a 100644
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--- a/module/zfs/zpl_super.c
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+++ b/module/zfs/zpl_super.c
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@@ -271,8 +271,17 @@ zpl_mount_impl(struct file_system_type *fs_type, int flags, zfs_mnt_t *zm)
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if (err)
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return (ERR_PTR(-err));
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+ /*
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+ * The dsl pool lock must be released prior to calling sget().
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+ * It is possible sget() may block on the lock in grab_super()
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+ * while deactivate_super() holds that same lock and waits for
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+ * a txg sync. If the dsl_pool lock is held over over sget()
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+ * this can prevent the pool sync and cause a deadlock.
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+ */
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+ dsl_pool_rele(dmu_objset_pool(os), FTAG);
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s = zpl_sget(fs_type, zpl_test_super, set_anon_super, flags, os);
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- dmu_objset_rele(os, FTAG);
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+ dsl_dataset_rele(dmu_objset_ds(os), FTAG);
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+
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if (IS_ERR(s))
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return (ERR_CAST(s));
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