From: Darrick J. Wong Date: Wed, 12 Apr 2023 05:49:10 +0000 (+1000) Subject: xfs: _{attr,data}_map_shared should take ILOCK_EXCL until iread_extents is completely... X-Git-Tag: v6.6.7~2856^2~35 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c95356ca884885db702670e24933ee7f2b9f1754;p=platform%2Fkernel%2Flinux-starfive.git xfs: _{attr,data}_map_shared should take ILOCK_EXCL until iread_extents is completely done While fuzzing the data fork extent count on a btree-format directory with xfs/375, I observed the following (excerpted) splat: XFS: Assertion failed: xfs_isilocked(ip, XFS_ILOCK_EXCL), file: fs/xfs/libxfs/xfs_bmap.c, line: 1208 ------------[ cut here ]------------ WARNING: CPU: 0 PID: 43192 at fs/xfs/xfs_message.c:104 assfail+0x46/0x4a [xfs] Call Trace: xfs_iread_extents+0x1af/0x210 [xfs 09f66509ece4938760fac7de64732a0cbd3e39cd] xchk_dir_walk+0xb8/0x190 [xfs 09f66509ece4938760fac7de64732a0cbd3e39cd] xchk_parent_count_parent_dentries+0x41/0x80 [xfs 09f66509ece4938760fac7de64732a0cbd3e39cd] xchk_parent_validate+0x199/0x2e0 [xfs 09f66509ece4938760fac7de64732a0cbd3e39cd] xchk_parent+0xdf/0x130 [xfs 09f66509ece4938760fac7de64732a0cbd3e39cd] xfs_scrub_metadata+0x2b8/0x730 [xfs 09f66509ece4938760fac7de64732a0cbd3e39cd] xfs_scrubv_metadata+0x38b/0x4d0 [xfs 09f66509ece4938760fac7de64732a0cbd3e39cd] xfs_ioc_scrubv_metadata+0x111/0x160 [xfs 09f66509ece4938760fac7de64732a0cbd3e39cd] xfs_file_ioctl+0x367/0xf50 [xfs 09f66509ece4938760fac7de64732a0cbd3e39cd] __x64_sys_ioctl+0x82/0xa0 do_syscall_64+0x2b/0x80 entry_SYSCALL_64_after_hwframe+0x46/0xb0 The cause of this is a race condition in xfs_ilock_data_map_shared, which performs an unlocked access to the data fork to guess which lock mode it needs: Thread 0 Thread 1 xfs_need_iread_extents xfs_ilock(..., ILOCK_EXCL) xfs_iread_extents xfs_need_iread_extents xfs_ilock(..., ILOCK_SHARED) xfs_iunlock(..., ILOCK_EXCL) xfs_iread_extents *BOOM* Fix this race by adding a flag to the xfs_ifork structure to indicate that we have not yet read in the extent records and changing the predicate to look at the flag state, not if_height. The memory barrier ensures that the flag will not be set until the very end of the function. Signed-off-by: Darrick J. Wong Reviewed-by: Dave Chinner Signed-off-by: Dave Chinner --- diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c index 34de6e6..f11ef33 100644 --- a/fs/xfs/libxfs/xfs_bmap.c +++ b/fs/xfs/libxfs/xfs_bmap.c @@ -1171,6 +1171,12 @@ xfs_iread_extents( goto out; } ASSERT(ir.loaded == xfs_iext_count(ifp)); + /* + * Use release semantics so that we can use acquire semantics in + * xfs_need_iread_extents and be guaranteed to see a valid mapping tree + * after that load. + */ + smp_store_release(&ifp->if_needextents, 0); return 0; out: xfs_iext_destroy(ifp); diff --git a/fs/xfs/libxfs/xfs_inode_fork.c b/fs/xfs/libxfs/xfs_inode_fork.c index 6b21760..1bbe5ea 100644 --- a/fs/xfs/libxfs/xfs_inode_fork.c +++ b/fs/xfs/libxfs/xfs_inode_fork.c @@ -226,10 +226,15 @@ xfs_iformat_data_fork( /* * Initialize the extent count early, as the per-format routines may - * depend on it. + * depend on it. Use release semantics to set needextents /after/ we + * set the format. This ensures that we can use acquire semantics on + * needextents in xfs_need_iread_extents() and be guaranteed to see a + * valid format value after that load. */ ip->i_df.if_format = dip->di_format; ip->i_df.if_nextents = xfs_dfork_data_extents(dip); + smp_store_release(&ip->i_df.if_needextents, + ip->i_df.if_format == XFS_DINODE_FMT_BTREE ? 1 : 0); switch (inode->i_mode & S_IFMT) { case S_IFIFO: @@ -282,8 +287,17 @@ xfs_ifork_init_attr( enum xfs_dinode_fmt format, xfs_extnum_t nextents) { + /* + * Initialize the extent count early, as the per-format routines may + * depend on it. Use release semantics to set needextents /after/ we + * set the format. This ensures that we can use acquire semantics on + * needextents in xfs_need_iread_extents() and be guaranteed to see a + * valid format value after that load. + */ ip->i_af.if_format = format; ip->i_af.if_nextents = nextents; + smp_store_release(&ip->i_af.if_needextents, + ip->i_af.if_format == XFS_DINODE_FMT_BTREE ? 1 : 0); } void diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h index d3943d6..96d3077 100644 --- a/fs/xfs/libxfs/xfs_inode_fork.h +++ b/fs/xfs/libxfs/xfs_inode_fork.h @@ -24,6 +24,7 @@ struct xfs_ifork { xfs_extnum_t if_nextents; /* # of extents in this fork */ short if_broot_bytes; /* bytes allocated for root */ int8_t if_format; /* format of this fork */ + uint8_t if_needextents; /* extents have not been read */ }; /* @@ -260,9 +261,10 @@ int xfs_iext_count_upgrade(struct xfs_trans *tp, struct xfs_inode *ip, uint nr_to_add); /* returns true if the fork has extents but they are not read in yet. */ -static inline bool xfs_need_iread_extents(struct xfs_ifork *ifp) +static inline bool xfs_need_iread_extents(const struct xfs_ifork *ifp) { - return ifp->if_format == XFS_DINODE_FMT_BTREE && ifp->if_height == 0; + /* see xfs_iformat_{data,attr}_fork() for needextents semantics */ + return smp_load_acquire(&ifp->if_needextents) != 0; } #endif /* __XFS_INODE_FORK_H__ */