Fix the update of the zero point[*] by netfs_release_folio() when there is uncommitted data in the pagecache beyond the folio being released but the on-server EOF is in this folio (ie. i_size > remote_i_size). The update needs to limit zero_point to remote_i_size, not i_size as i_size is a local phenomenon reflecting updates made locally to the pagecache, not stuff written to the server. remote_i_size tracks the server's i_size. [*] The zero point is the file position from which we can assume that the server will just return zeros, so we can avoid generating reads. Note that netfs_invalidate_folio() probably doesn't need fixing as zero_point should be updated by setattr after truncation or fallocate. Found with: fsx -q -N 1000000 -p 10000 -o 128000 -l 600000 \ /xfstest.test/junk --replay-ops=junk.fsxops using the following as junk.fsxops: truncate 0x0 0x1bbae 0x82864 write 0x3ef2e 0xf9c8 0x1bbae write 0x67e05 0xcb5a 0x4e8f6 mapread 0x57781 0x85b6 0x7495f copy_range 0x5d3d 0x10329 0x54fac 0x7495f write 0x64710 0x1c2b 0x7495f mapread 0x64000 0x1000 0x7495f on cifs with the default cache option. It shows read-gaps on folio 0x64 failing with a short read (ie. it hits EOF) if the FMODE_READ check is commented out in netfs_perform_write(): if (//(file->f_mode & FMODE_READ) || netfs_is_cache_enabled(ctx)) { and no fscache. This was initially found with the generic/522 xfstest. Fixes: cce6bfa6ca0e ("netfs: Fix trimming of streaming-write folios in netfs_inval_folio()") Signed-off-by: David Howells cc: Paulo Alcantara cc: Matthew Wilcox cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org --- fs/netfs/misc.c | 4 ++-- include/linux/netfs.h | 35 +++++++++++++++++++++++++++-------- 2 files changed, 29 insertions(+), 10 deletions(-) diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c index 9d92d068f1da..37d9651078e6 100644 --- a/fs/netfs/misc.c +++ b/fs/netfs/misc.c @@ -299,9 +299,9 @@ bool netfs_release_folio(struct folio *folio, gfp_t gfp) return false; netfs_read_sizes(ctx, &i_size, &remote_i_size, &zero_point); - end = umin(folio_next_pos(folio), i_size); + end = folio_next_pos(folio); if (end > zero_point) - netfs_write_zero_point(ctx, end); + netfs_push_back_zero_point(ctx, umin(end, remote_i_size)); if (folio_test_private(folio)) return false; diff --git a/include/linux/netfs.h b/include/linux/netfs.h index 90e061e444ce..59f35d2eeb2e 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -530,11 +530,11 @@ static inline void netfs_write_remote_i_size(struct netfs_inode *ictx, #if BITS_PER_LONG==32 && defined(CONFIG_SMP) struct inode *inode = &ictx->inode; - preempt_disable(); + spin_lock(&inode->i_lock); write_seqcount_begin(&inode->i_size_seqcount); ictx->_remote_i_size = remote_i_size; write_seqcount_end(&inode->i_size_seqcount); - preempt_enable(); + spin_unlock(&inode->i_lock); #elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) preempt_disable(); ictx->_remote_i_size = remote_i_size; @@ -605,11 +605,11 @@ static inline void netfs_write_zero_point(struct netfs_inode *ictx, #if BITS_PER_LONG==32 && defined(CONFIG_SMP) struct inode *inode = &ictx->inode; - preempt_disable(); + spin_lock(&inode->i_lock); write_seqcount_begin(&inode->i_size_seqcount); ictx->_zero_point = zero_point; write_seqcount_end(&inode->i_size_seqcount); - preempt_enable(); + spin_unlock(&inode->i_lock); #elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) preempt_disable(); ictx->_zero_point = zero_point; @@ -635,8 +635,27 @@ static inline void netfs_write_zero_point(struct netfs_inode *ictx, static inline void netfs_push_back_zero_point(struct netfs_inode *ictx, unsigned long long to) { - if (to > netfs_read_zero_point(ictx)) - netfs_write_zero_point(ictx, to); +#if BITS_PER_LONG==32 && defined(CONFIG_SMP) + struct inode *inode = &ictx->inode; + + spin_lock(&inode->i_lock); + write_seqcount_begin(&inode->i_size_seqcount); + if (to > ictx->_zero_point) + ictx->_zero_point = to; + write_seqcount_end(&inode->i_size_seqcount); + spin_unlock(&inode->i_lock); +#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) + preempt_disable(); + if (to > ictx->_zero_point) + ictx->_zero_point = to; + preempt_enable(); +#else + unsigned long long old = ictx->_zero_point; + + while (to > old) { + old = cmpxchg_release(&ictx->_zero_point, old, to); + } +#endif } /** @@ -709,12 +728,12 @@ static inline void netfs_write_sizes(struct netfs_inode *ictx, #if BITS_PER_LONG==32 && defined(CONFIG_SMP) struct inode *inode = &ictx->inode; - preempt_disable(); + spin_lock(&inode->i_lock); write_seqcount_begin(&inode->i_size_seqcount); ictx->_remote_i_size = remote_i_size; ictx->_zero_point = zero_point; write_seqcount_end(&inode->i_size_seqcount); - preempt_enable(); + spin_unlock(&inode->i_lock); #elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) preempt_disable(); ictx->_remote_i_size = remote_i_size;