fuse: hold i_mutex in fuse_file_fallocate()
Changing size of a file on server and local update (fuse_write_update_size) should be always protected by inode->i_mutex. Otherwise a race like this is possible: 1. Process 'A' calls fallocate(2) to extend file (~FALLOC_FL_KEEP_SIZE). fuse_file_fallocate() sends FUSE_FALLOCATE request to the server. 2. Process 'B' calls ftruncate(2) shrinking the file. fuse_do_setattr() sends shrinking FUSE_SETATTR request to the server and updates local i_size by i_size_write(inode, outarg.attr.size). 3. Process 'A' resumes execution of fuse_file_fallocate() and calls fuse_write_update_size(inode, offset + length). But 'offset + length' was obsoleted by ftruncate from previous step. Changed in v2 (thanks Brian and Anand for suggestions): - made relation between mutex_lock() and fuse_set_nowrite(inode) more explicit and clear. - updated patch description to use ftruncate(2) in example Signed-off-by: Maxim V. Patlasov <MPatlasov@parallels.com> Reviewed-by: Brian Foster <bfoster@redhat.com> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
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Коммит
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@ -2470,13 +2470,16 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
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.mode = mode
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.mode = mode
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};
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};
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int err;
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int err;
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bool lock_inode = !(mode & FALLOC_FL_KEEP_SIZE) ||
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(mode & FALLOC_FL_PUNCH_HOLE);
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if (fc->no_fallocate)
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if (fc->no_fallocate)
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return -EOPNOTSUPP;
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return -EOPNOTSUPP;
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if (mode & FALLOC_FL_PUNCH_HOLE) {
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if (lock_inode) {
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mutex_lock(&inode->i_mutex);
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mutex_lock(&inode->i_mutex);
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fuse_set_nowrite(inode);
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if (mode & FALLOC_FL_PUNCH_HOLE)
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fuse_set_nowrite(inode);
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}
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}
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req = fuse_get_req_nopages(fc);
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req = fuse_get_req_nopages(fc);
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@ -2511,8 +2514,9 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
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fuse_invalidate_attr(inode);
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fuse_invalidate_attr(inode);
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out:
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out:
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if (mode & FALLOC_FL_PUNCH_HOLE) {
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if (lock_inode) {
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fuse_release_nowrite(inode);
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if (mode & FALLOC_FL_PUNCH_HOLE)
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fuse_release_nowrite(inode);
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mutex_unlock(&inode->i_mutex);
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mutex_unlock(&inode->i_mutex);
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}
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}
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